Input circuit, output circuit, input-output circuit and method of processing input signals

• US 6,294,932 B1
• Filed: 12/06/1999
• Issued: 09/25/2001
• Est. Priority Date: 12/07/1998
• Status: Expired due to Term

• Current Assignee: Renesas Electronics Corporation
• Original Assignee: NEC Corporation
• Inventors: Watarai, Seiichi
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): Tran, Anh Q.
• Application Number:
  US09/455,028
• Time in Patent Office: 659 Days
• Field of Search: 326/86, 326/82, 326/83, 326/66, 326/68, 326/73, 326/69, 326/90
• US Class Current: 326/83
• CPC Class Codes: H03K 19/00384 in field effect transistor circuits
• CPC Class Codes: H03K 19/018528 with at least one differential stage
• CPC Class Codes: H04L 25/0272 Arrangements for coupling to multiple lines, e.g. for differential transmission
• CPC Class Codes: H04L 25/028 Arrangements specific to the transmitter end
• CPC Class Codes: H04L 25/0292 Arrangements specific to the receiver end

Abstract

An input-output circuit in which, even if variations in logic threshold voltages occurs, a logic signal can be exactly recognized on the basis of small-amplitude signals supplied. The input-output circuit of the present invention contains a threshold value detecting circuit, an amplifying section used to output a voltage having amplitude center level of a small-amplitude signal, to amplify the small-amplitude signal to a predetermined amplitude level, to convert the small-amplitude signal to a logic signal (rectangular wave) that can be processed by a CMOS internal circuit and to feed the converted signal through an output terminal to the CMOS internal circuit, a constant current circuit used to change amplification factor of the small-amplitude signal inputted, and a feedback amplifier to compare the amplitude center voltage of the small-amplitude signal with a voltage supplied from the threshold value detectt ing circuit and to feedback a voltage to the constant current circuit so that the amplitude center voltage of the signal amplified by the amplifying section is equal to a voltage set by the threshold value detectt ing circuit.

Claims

1. An input circuit for transmitting a signal between semiconductor devices with an input stage and an output stage, said input circuit comprising:

a threshold value detecting means to detect a threshold value of said output stage; and

a feedback amplifier that compares the threshold value and an amplitude center level of a signal fed from said input stage to said output stage such that said amplitude center level voltage can be made equal to said threshold value detected by said threshold value detecting means.

2. The input circuit according to claim 1, wherein said threshold value detecting means of said output stage has a threshold value being equivalent to that of said output stage.

3. The input circuit according to claim 1, wherein said threshold value detecting means of said output stage is composed of a CMOS logic circuit having two or more transistors within a same integrated circuit produced by a same manufacturing processes and mounted on a same board.

4. The input circuit according to claim 3, wherein said CMOS circuit is comprised of more than one nMOS transistor and more than one pMOS transistor.

5. An input circuit according to claim 1, wherein an amplitude of an output signal fed from said input stage to said output stage is equal to or more than that of said input signal fed to said input stage.

6. An input circuit according to claim 1, wherein an amplitude of an output signal fed from said input stage to said output stage is equal to or less than that of said input signal fed to said input stage.

7. An input circuit for transmitting a signal between semiconductor devices with an input stage and an output stage, input circuit comprising:

a threshold value detecting means to detect a threshold value of said output stage;

whereby said threshold value of said output stage detected by said threshold value detecting means and an amplitude center level of a signal fed to said stage from said input stage are detected and compared and whereby currents to be supplied to said input stage are controlled so that both said values are equal, and an amplitude center level of a signal fed from said input stage is determined in accordance with variations in said threshold value of said output stage detected by said threshold value detecting means.

8. The input circuit according to claim 7, wherein said threshold value detecting means of said output stage has a threshold value being equivalent to that of said output stage.

9. The input circuit according to claim 7, wherein said threshold value detecting means of said output stage is composed of a CMOS logic circuit having two or more transistors within a same integrated circuit produced by a same manufacturing processes and mounted on a same board.

10. The input circuit according to claim 9, wherein said CMOS circuit is comprised of more than one nMOS transistor and more than one pMOS transistor.

11. An input circuit according to claim 7, wherein an amplitude of an output signal fed from said input stage to said output stage is equal to or more than that of said input signal fed to said input stage.

12. An input circuit according to claim 7, wherein an amplitude of an output signal fed from said input stage to said output stage is equal to or less than that of said input signal fed to said input stage.

13. An input circuit for transmitting a signal between semiconductor devices with an input stage and an output stage wherein an amplitude center level of an output signal from said input stage is converted to a level corresponding to variations in a threshold value of said output stage and the converted signal is fed to said output stage.

14. An input circuit according to claim 13, wherein an amplitude of an output signal fed from said input stage to said output stage is equal to or more than that of said input signal fed to said input stage.

15. An input circuit according to claim 13, wherein an amplitude of an output signal fed from said input stage to said output stage is equal to or less than that of said input signal fed to said input stage.

16. A method for processing an input signal in an input circuit used for transmitting a signal between semiconductor devices and provided with an input stage and an output stage, said method comprising the step of:

changing an amplitude center value of an output signal fed from said input stage to said output stage depending on variations in a threshold value of said output stage.

17. An output circuit for transmitting a signal between semiconductor devices wherein a signal fed to said output circuit is converted to a signal having a predetermined amplitude level and an amplitude center level to produce a small-amplitude signal for transmission.

18. An input-output circuit used between semiconductor devices connected through transmission lines comprising:

an output circuit for transmitting a signal between semiconductor devices wherein a signal fed to said output circuit is converted to a signal having a predetermined amplitude level and an amplitude center level to produce a small-amplitude signal for transmission;

an input circuit for transmitting a signal between semiconductor devices with an input stage and an output stage, said input circuit comprising a threshold value detecting means to detect a threshold value of said output stage;

a feedback amplifier that compares the threshold value and an amplitude center level, whereby the amplitude level of a signal fed from said input stage to said output stage is amplified in accordance with said threshold value detected by said threshold value detecting means; and

transmission lines to connect said output circuit to said input circuit.

19. An input-output circuit used between semiconductor devices connected through transmission lines comprising:

an output circuit for transmitting a signal between semiconductor devices wherein a signal fed to said output circuit is converted to a signal having a predetermined amplitude level and an amplitude center level to produce a small-amplitude signal for transmission;

an input circuit for transmitting a signal between semiconductor devices with an input stage and an output stage, comprising a threshold value detecting means to detect a threshold value of said output stage, whereby said threshold value of said output stage detected by said threshold value detecting means and an amplitude center level of a signal fed to said stage from said input stage are detected and compared and whereby currents to be supplied to said input stage are controlled so that said threshold value and amplitude center level are equal, and said amplitude center level of said signal fed from input stage is determined in accordance with variations in said threshold value of said output stage detected by said threshold value detecting means; and

transmission lines to connect said output circuit to said input circuit.

20. An input-output circuit used between semiconductor devices connected through transmission lines comprising:

an output circuit for transmitting a signal between semiconductor devices wherein a signal fed to said output circuit is converted to a signal having a predetermined amplitude level and an amplitude center level to produce a small-amplitude signal for transmission;

an input circuit for transmitting a signal between semiconductor devices with an input stage and an output stage wherein an amplitude center level of an output signal corresponding to variations in a threshold value of said output stage and the converted signal is fed to said output stage; and

transmission lines to connect said output circuit to said input circuit.

21. An input circuit for transmitting a signal between semiconductor devices, amplifying a supplied small-amplitude signal to a full-swing amplitude level being equal to or near to that of a power supply voltage and feeding it as a logic signal, said input circuit comprising:

an amplifying section to output an amplitude center voltage of said small-amplitude signal and converting said small-amplitude signal by amplification to a logic signal having a predetermined amplitude level;

a threshold value detecting means to detect a signal inversion point voltage of a CMOS logic circuit receiving an output signal from said amplifying section;

a constant current circuit to control amplification factor and amplified signal amplitude center level in said amplifying section; and

a feedback amplifier to compare a signal amplitude center voltage outputted from said amplifying section with a signal inversion point voltage of said CMOS logic circuit detected by said threshold value detecting means and to feed a voltage back to said constant current circuit so that an amplitude center level of a signal amplified by said amplifying section is equal to said signal inversion point voltage of said CMOS logic circuit.

22. The input circuit according to claim 21, wherein said threshold value detecting means has a same circuit configuration as said CMOS logic circuit, which is comprised of two or more transistors, each being mounted on a same integrated circuit and on a same board and being produced by a same manufacturing processes.

23. The input circuit according to claim 21, wherein said threshold value detecting means has a threshold value being equivalent to that of said CMOS logic circuit.

24. The input circuit according to claim 21, wherein said threshold value detecting means is composed of a CMOS logic circuit having two or more transistors within a same integrated circuit produced by a same manufacturing processes and mounted on a same board.

25. The input circuit according to claim 21, wherein said CMOS circuit is comprised of more than one nMOS transistor and more than one pMOS transistor.

26. The input circuit according to according to claim 21, wherein said CMOS circuit is a CMOS inverter circuit.

27. An input circuit for transmitting a signal between semiconductor devices, amplifying a supplied small-amplitude signal to a full-swing amplitude level being equal to or near to that of a power supply voltage and feeding it as a logic signal, said input circuit comprising:

an amplitude center voltage detecting means to detect the amplitude center level of said small-amplitude signal;

an amplifying circuit to convert said small-amplitude signal by amplification to a logic signal having a predetermined amplitude level;

a constant current circuit to control amplification factor and amplified signal amplitude center level in said amplifying circuit;

a CMOS logic circuit to convert a signal amplified by said amplifying circuit to said logic signal;

a threshold value detecting means to a signal inversion point voltage of said CMOS logic circuit; and

a feedback amplifier to compare an amplitude center level detected by said amplitude center voltage detecting means with a signal inversion point voltage of said CMOS logic circuit detected by said threshold value detecting means and to feed a voltage back to said constant current circuit so that an amplitude center voltage of a signal to be amplified by said amplifying circuit is equal to a signal inversion point voltage of said CMOS logic circuit.

28. The input circuit according to claim 27, wherein said threshold value detecting means has a same circuit configuration as said CMOS logic circuit, which is comprised of two or more transistors, each being mounted on a same integrated circuit and on a same board and being produced by a same manufacturing processes.

29. The input circuit according to claim 27, wherein said threshold value detecting means has a threshold value being equivalent to that of said CMOS logic circuit.

30. The input circuit according to claim 27, wherein said threshold value detecting means is composed of a CMOS logic circuit having two or more transistors within a same integrated circuit produced by a same manufacturing processes and mounted on a same board.

31. The input circuit according to claim 27, wherein said CMOS circuit is comprised of more than one nMOS transistor and more than one pMOS transistor.

32. The input circuit according to according to claim 27, wherein said CMOS circuit is a CMOS inverter circuit.

33. An input circuit for transmitting a signal between semiconductor devices, amplifying a supplied small-amplitude signal to a full-swing amplitude level being equal to or near to that of a power supply voltage and feeding it as a logic signal, said input circuit comprising:

a level conversion circuit to control a center level of said small-amplitude signal;

an amplitude center voltage detecting means to detect an amplitude center level of a signal fed from said level conversion circuit;

a threshold value detecting means to detect a signal inversion point voltage of a CMOS logic circuit receiving an output signal from said level conversion circuit;

a constant current circuit to control amounts of voltage to be shifted by said level conversion circuit; and

a feedback amplifier to compare an amplitude center voltage outputted by said level conversion circuit with a signal inversion point voltage of said CMOS logic circuit detected by said threshold value detecting means and to feed a voltage back to said constant current circuit so that an amplitude center voltage outputted from said level conversion circuit is equal to a signal inversion point voltage of said CMOS logic circuit.

34. The input circuit according to claim 33, wherein said threshold value detecting means has a same circuit configuration as said CMOS logic circuit, which is comprised of two or more transistors, each being mounted on a same integrated circuit and on a same board and being produced by a same manufacturing processes.

35. The input circuit according to claim 33, wherein said threshold value detecting means has a threshold value being equivalent to that of said CMOS logic circuit.

36. The input circuit according to claim 33, wherein said threshold value detecting means is composed of a CMOS logic circuit having two or more transistors within a same integrated circuit produced by a same manufacturing processes and mounted on a same board.

37. The input circuit according to claim 33, wherein said CMOS circuit is comprised of more than one nMOS transistor and more than one pMOS transistor.

38. The input circuit according to according to claim 33, wherein said CMOS circuit is a CMOS inverter circuit.

39. An input circuit for transmitting a signal between semiconductor devices, amplifying a supplied small-amplitude signal to a full-swing amplitude level being equal to or near to that of a power supply voltage and feeding it as a logic signal, said input circuit comprising:

a level conversion circuit to control a center level of said small-amplitude signal;

an amplitude center voltage detecting means to detect a signal amplitude center voltage supplied from said level conversion circuit;

a mos logic circuit to convert a signal having a level shifted by said level conversion circuit to said logic signal;

a threshold value detecting means to detect a signal inversion point voltage of said CMOS logic circuit;

a constant current circuit to control amounts of voltage to be shifted by said level conversion circuit; and

a feedback amplifier to compare an amplitude center voltage outputted by said amplitude center voltage detecting means with a signal inversion point voltage of said CMOS logic circuit detected by said threshold value detecting means and to feed a voltage back to said constant current circuit so that an amplitude center voltage outputted from said level conversion circuit is equal to a signal inversion point voltage of said CMOS logic circuit.

40. The input circuit according to claim 39, wherein said threshold value detecting means has a same circuit configuration as said CMOS logic circuit, which is comprised of two or more transistors, each being mounted on a same integrated circuit and on a same board and being produced by a same manufacturing processes.

41. The input circuit according to claim 39, wherein said threshold value detecting means has a threshold value being equivalent to that of said CMOS logic circuit.

42. The input circuit according to claim 39, wherein said threshold value detecting means is composed of a CMOS logic circuit having two or more transistors within a same integrated circuit produced by a same manufacturing processes and mounted on a same board.

43. The input circuit according to claim 39, wherein said CMOS circuit is comprised of more than one nMOS transistor and more than one pMOS transistor.

44. The input circuit according to according to claim 39, wherein said CMOS circuit is a CMOS inverter circuit.

45. An output circuit for transmitting a signal between semiconductor devices, converting a su supplied input signal to a small-amplitude transmission signal on the basis of a specified small-amplitude interfacing specifications and feeding it, said output circuit comprising:

a constant voltage generating means to generate a voltage used to set an output center level of said small-amplitude transmission signal;

an output section to detect an output center level from said output transmission signal and to convert an amplitude of said output transmission signal to a predetermined amplitude; and

a feedback amplifier to compare an output center level outputted by a constant voltage circuit used to shift an output center level of said supplied transmission signal and by said output section with a voltage generated by said constant voltage generating means and to feed a voltage back to said constant current circuit so that an output center level of a small-amplitude signal outputted from said output section is equal to a voltage value set by said constant voltage generating means.

46. An output circuit for transmitting a signal between semiconductor devices, converting a supplied input signal to a small-amplitude transmission signal on the basis of a specified small-amplitude interfacing specifications and feeding it, said output circuit comprising:

a reference voltage generating means used to produce an output center level voltage of said small-amplitude transmission signal;

an output center voltage detecting means to detect an output center level from said output transmission signal;

a constant voltage circuit used to shift an output center level of said output transmission signal;

a feedback amplifier to compare an output center level detected by said output center voltage detecting means with a voltage generated by said reference voltage generating means and to feed a voltage back to said constant current circuit so that an output center level of said output transmission signal is equal to a voltage value set by said reference voltage generating means; and

an amplitude level changing means to convert an amplitude of said supplied input signal to a predetermined small-amplitude level.

47. An input-output circuit used between semiconductor devices connected through transmission lines comprising:

an input circuit for transmitting a signal between semiconductor devices, amplifying a supplied small-amplitude signal to a fill-swing amplitude level being equal to or near to that of a power supply voltage and feeding it as a logic signal, said input circuit comprising;

an amplifying section to output an amplitude center voltage of said small-amplitude signal and converting said small-amplitude signal by amplification to a logic signal having a predetermined amplitude level;

a threshold value detecting means to detect a signal inversion point voltage of a CMOS logic circuit receiving an output signal from said amplifying section;

a constant current circuit to control amplification factor and amplified signal amplitude center level in said amplifying section; and

a feedback amplifier to compare a signal amplitude center voltage outputted from said amplifying section with a signal inversion point voltage of said CMOS logic circuit detected by said threshold value detecting means and to feed a voltage back to said constant current circuit so that an amplitude center level of a signal amplified by said amplifying section is equal to said signal inversion point voltage of said CMOS logic circuit;

an output circuit for transmitting a signal between semiconductor devices, converting a supplied input signal to a small-amplitude transmission signal on the basis of a specified small-amplitude interfacing specifications and feeding it, said output circuit comprising;

a constant voltage generating means to generate a voltage used to set an output center level of said small-amplitude transmission signal;

an output section to detect an output center level from said output transmission signal and to convert an amplitude of said output transmission signal to a predetermined amplitude; and

a feedback amplifier to compare an output center level outputted by a constant voltage circuit used to shift an output center level of said supplied transmission signal and by said output section with a voltage generated by said constant voltage generating means and to feed a voltage back to said constant current circuit so that an output center level of a smallamplitude signal outputted from said output section is equal to a voltage value set by said constant voltage generating means; and

transmission lines to connect said output circuit to said input circuit.

48. An input-output circuit used between semiconductor devices connected through transmission lines comprising:

an input circuit for transmitting a signal between semiconductor devices, amplifying a supplied small-amplitude signal to a full-swing amplitude level being equal to or near to that of a power supply voltage and feeding it as a logic signal, said input circuit comprising;

an amplitude center voltage detecting means to detect the amplitude center level of said small-amplitude signal;

an amplifying circuit to convert said small-amplitude signal by amplification to a logic signal having a predetermined amplitude level;

a constant current circuit to control amplification factor and amplified signal amplitude center level in said amplifying circuit;

a CMOS logic circuit to convert a signal amplified by said amplifying circuit to said logic signal;

a threshold value detecting means to a signal inversion point voltage of said CMOS logic circuit; and

a feedback amplifier to compare an amplitude center level detected by said amplitude center voltage detecting means with a signal inversion point voltage of said CMOS logic circuit detected by said threshold value detecting means and to feed a voltage back to said constant current circuit so that an amplitude center voltage of a signal to be amplified by said amplifying circuit is equal to a signal inversion point voltage of said CMOS logic circuit;

an output circuit for transmitting a signal between semiconductor devices, converting a supplied input signal to a small-amplitude transmission signal on the basis of a specified small-amplitude interfacing specifications and feeding it, said output circuit comprising;

a constant voltage generating means to generate a voltage used to set an output center level of said small-amplitude transmission signal;

an output section to detect an output center level from said output transmission signal and to convert an amplitude of said output transmission signal to a predetermined amplitude; and

a feedback amplifier to compare an output center level outputted by a constant voltage circuit used to shift an output center level of said supplied transmission signal and by said output section with a voltage generated by said constant voltage generating means and to feed a voltage back to said constant current circuit so that an output center level of a small-amplitude signal outputted from said output section is equal to a voltage value set by said constant voltage generating means; and

transmission lines to connect said output circuit to said input circuit.

49. An input-output circuit used between semiconductor devices connected through transmission lines comprising:

an input circuit for transmitting a signal between semiconductor devices, amplifying a supplied small-amplitude signal to a full-swing amplitude level being equal to or near to that of a power supply voltage and feeding it as a logic signal, said input circuit comprising;

a level conversion circuit to control a center level of said small-amplitude signal;

an amplitude center voltage detecting means to an amplitude center level of a signal fed from said level conversion circuit;

a threshold value detecting means to detect a signal inversion point voltage of a CMOS logic circuit receiving an output signal from said level conversion circuit;

a constant current circuit to control amounts of voltage to be shifted by said level conversion circuit; and

a feedback amplifier to compare an amplitude center voltage outputted by said level conversion circuit with a signal inversion point voltage of said CMOS logic circuit detected by said threshold value detecting means and to feed a voltage back to said constant current circuit so that an amplitude center voltage outputted from said level conversion circuit is equal to a signal inversion point voltage of said CMOS logic circuit;

an output circuit for transmitting a signal between semiconductor devices, converting a supplied input signal to a small-amplitude transmission signal on the basis of a specified small-amplitude interfacing specifications and feeding it, said output circuit comprising;

a constant voltage generating means to generate a voltage used to set an output center level of said small-amplitude transmission signal;

an output section to detect an output center level from said output transmission signal and to convert an amplitude of said output transmission signal to a predetermined amplitude; and

a feedback amplifier to compare an output center level outputted by a constant voltage circuit used to shift an output center level of said supplied transmission signal and by said output section with a voltage generated by said constant voltage generating means and to feed a voltage back to said constant current circuit so that an output center level of a small-amplitude signal outputted from said output section is equal to a voltage value set by said constant voltage generating means; and

transmission lines to connect said output circuit to said input circuit.

50. An input-output circuit used between semiconductor devices connected through transmission lines comprising:

an input circuit for transmitting a signal between semiconductor devices, amplifying a supplied small-amplitude signal to a full-swing amplitude level being equal to or near to that of a power supply voltage and feeding it as a logic signal, said input circuit comprising;

a level conversion circuit to control a center level of said small-amplitude signal;

an amplitude center voltage detecting means to detect a signal amplitude center voltage supplied from said level conversion circuit;

a CMOS logic circuit to convert a signal having a level shifted by said level conversion circuit to said logic signal;

a threshold value detecting means to detect a signal inversion point voltage of said CMOS logic circuit;

a constant current circuit to control amounts of voltage to be shifted by said level conversion circuit; and

a feedback amplifier to compare an amplitude center voltage outputted by said amplitude center voltage detecting means with a signal inversion point voltage of said CMOS logic circuit detected by said threshold value detecting means and to feed a voltage back to said constant current circuit so that an amplitude center voltage outputted from said level conversion circuit is equal to a signal inversion point voltage of said CMOS logic circuit;

an output circuit for transmitting a signal between semiconductor devices, converting a supplied input signal to a small-amplitude transmission signal on the basis of a specified small-amplitude interfacing specifications and feeding it, said output circuit comprising;

a constant voltage generating means to generate a voltage used to set an output center level of said small-amplitude transmission signal;

an output section to detect an output center level from said output transmission signal and to convert an amplitude of said output transmission signal to a predetermined amplitude; and

a feedback amplifier to compare an output center level outputted by a constant voltage circuit used to shift an output center level of said supplied transmission signal and by said output section with a voltage generated by said constant voltage generating means and to feed a voltage back to said constant current circuit so that an output center level of a smallamplitude signal outputted from said output section is equal to a voltage value set by said constant voltage generating means; and

transmission lines to connect said output circuit to said input circuit.

51. An input-output circuit used between semiconductor devices connected through transmission lines comprising:

an input circuit for transmitting a signal between semiconductor devices, amplifying a supplied small-amplitude signal to a full-swing amplitude level being equal to or near to that of a power supply voltage and feeding it as a logic signal, said input circuit comprising;

an amplifying section to output an amplitude center voltage of said small-amplitude signal and converting said small-amplitude signal by amplification to a logic signal having a predetermined amplitude level;

a threshold value detecting means to detect a signal inversion point voltage of a CMOS logic circuit receiving an output signal from said amplifying section;

a constant current circuit to control amplification factor and amplified signal amplitude center level in said amplifying section; and

a feedback amplifier to compare a signal amplitude center voltage outputted from said amplifying section with a signal inversion point voltage of said CMOS logic circuit detected by said threshold value detecting means and to feed a voltage back to said constant current circuit so that an amplitude center level of a signal amplified by said amplifying section is equal to said signal inversion point voltage of said CMOS logic circuit;

an output circuit for transmitting a signal between semiconductor devices, converting a supplied input signal to a small-amplitude transmission signal on the basis of a specified small-amplitude interfacing specifications and feeding it, said output circuit comprising;

a reference voltage generating means used to produce an output center level voltage of said small-amplitude transmission signal;

an output center voltage detecting means to detect an output center level from said output transmission signal;

a constant voltage circuit used to shift an output center level of said output transmission signal;

a feedback amplifier to compare an output center level detected by said output center voltage detecting means with a voltage generated by said reference voltage generating means and to feed a voltage back to said constant current circuit so that an output center level of said output transmission signal is equal to a voltage value set by said reference voltage generating means; and

an amplitude level changing means to convert an amplitude of said supplied input signal to a predetermined small-amplitude level; and

transmission lines to connect said output circuit to said input circuit.

52. An input-output circuit used between semiconductor devices connected through transmission lines comprising:

an input circuit for transmitting a signal between semiconductor devices, amplifying a supplied small-amplitude signal to a full-swing amplitude level being equal to or near to that of a power supply voltage and feeding it as a logic signal, said input circuit comprising;

an amplitude center voltage detecting means to detect the amplitude center level of said small-amplitude signal;

an amplifying circuit to convert said small-amplitude signal by amplification to a logic signal having a predetermined amplitude level;

a constant current circuit to control amplification factor and amplified signal amplitude center level in said amplifying circuit;

a CMOS logic circuit to convert a signal amplified by said amplifying circuit to said logic signal;

a threshold value detecting means to a signal inversion point voltage of said CMOS logic circuit; and

a feedback amplifier to compare an amplitude center level detected by said amplitude center voltage detecting means with a signal inversion point voltage of said CMOS logic circuit detected by said threshold value detecting means and to feed a voltage back to said constant current circuit so that an amplitude center voltage of a signal to be amplified by said amplifying circuit is equal to a signal inversion point voltage of said CMOS logic circuit;

an output circuit for transmitting a signal between semiconductor devices, converting a supplied input signal to a small-amplitude transmission signal on the basis of a specified small-amplitude interfacing specifications and feeding it, said output circuit comprising;

a reference voltage generating means used to produce an output center level voltage of said small-amplitude transmission signal;

an output center voltage detecting means to detect an output center level from said output transmission signal;

a constant voltage circuit used to shift an output center level of said output transmission signal;

a feedback amplifier to compare an output center level detected by said output center voltage detecting means with a voltage generated by said reference voltage generating means and to feed a voltage back to said constant current circuit so that an output center level of said output transmission signal is equal to a voltage value set by said reference voltage generating means; and

an amplitude level changing means to convert an amplitude of said supplied input signal to a predetermined small-amplitude level; and

transmission lines to connect said output circuit to said input circuit.

53. An input-output circuit used between semiconductor devices connected through transmission lines comprising:

an input circuit for transmitting a signal between semiconductor devices, amplifying a supplied small-amplitude signal to a full-swing amplitude level being equal to or near to that of a power supply voltage and feeding it as a logic signal, said input circuit comprising;

a level conversion circuit to control a center level of said small-amplitude signal;

an amplitude center voltage detecting means to an amplitude center level of a signal fed from said level conversion circuit;

a threshold value detecting means to detect a signal inversion point voltage of a CMOS logic circuit receiving an output signal from said level conversion circuit;

a constant current circuit to control amounts of voltage to be shifted by said level conversion circuit; and

a feedback amplifier to compare an amplitude center voltage outputted by said level conversion circuit with a signal inversion point voltage of said CMOS logic circuit detected by said threshold value detecting means and to feed a voltage back to said constant current circuit so that an amplitude center voltage outputted from said level conversion circuit is equal to a signal inversion point voltage of said CMOS logic circuit;

an output circuit for transmitting a signal between semiconductor devices, converting a supplied input signal to a small-amplitude transmission signal on the basis of a specified small-amplitude interfacing specifications and feeding it, said output circuit comprising;

a reference voltage generating means used to produce an output center level voltage of said small-amplitude transmission signal;

an output center voltage detecting means to detect an output center level from said output transmission signal;

a constant voltage circuit used to shift an output center level of said output transmission signal;

a feedback amplifier to compare an output center level detected by said output center voltage detecting means with a voltage generated by said reference voltage generating means and to feed a voltage back to said constant current circuit so that an output center level of said output transmission signal is equal to a voltage value set by said reference voltage generating means; and

an amplitude level changing means to convert an amplitude of said supplied input signal to a predetermined small-amplitude level; and

transmission lines to connect said output circuit to said input circuit.

54. An input-output circuit used between semiconductor devices connected through transmission lines comprising:

an input circuit for transmitting a signal between semiconductor devices, amplifying a supplied small-amplitude signal to a full-swing amplitude level being equal to or near to that of a power supply voltage and feeding it as a logic signal, said input circuit comprising;

a level conversion circuit to control a center level of said small-amplitude signal;

an amplitude center voltage detecting means to detect a signal amplitude center voltage supplied from said level conversion circuit;

a CMOS logic circuit to convert a signal having a level shifted by said level conversion circuit to said logic signal;

a threshold value detecting means to detect a signal inversion point voltage of said CMOS logic circuit;

a constant current circuit to control amounts of voltage to be shifted by said level conversion circuit; and

a feedback amplifier to compare an amplitude center voltage outputted by said amplitude center voltage detecting means with a signal inversion point voltage of said CMOS logic circuit detected by said threshold value detecting means and to feed a voltage back to said constant current circuit so that an amplitude center voltage outputted from said level conversion circuit is equal to a signal inversion point voltage of said CMOS logic circuit;

an output circuit for transmitting a signal between semiconductor devices, converting a supplied input signal to a small-amplitude transmission signal on the basis of a specified small-amplitude interfacing specifications and feeding it, said output circuit comprising;

a reference voltage generating means used to produce an output center level voltage of said small-amplitude transmission signal;

an output center voltage detecting means to detect an output center level from said output transmission signal;

a constant voltage circuit used to shift an output center level of said output transmission signal;

a feedback amplifier to compare an output center level detected by said output center voltage detecting means with a voltage generated by said reference voltage generating means and to feed a voltage back to said constant current circuit so that an output center level of said output transmission signal is equal to a voltage value set by said reference voltage generating means; and

an amplitude level changing means to convert an amplitude of said supplied input signal to a predetermined small-amplitude level; and

transmission lines to connect said output circuit to said input circuit.