High speed bus system

• US 5,355,391 A
• Filed: 03/06/1992
• Issued: 10/11/1994
• Est. Priority Date: 03/06/1992
• Status: Expired due to Term

• Current Assignee: Rambus Inc.
• Original Assignee: Rambus Inc.
• Inventors: Horowitz, Mark A., Lee, Winston K. M.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): WEBSTER, BRYAN E
• Application Number:
  US07/847,635
• Time in Patent Office: 949 Days
• Field of Search: 375/36, 307/475, 307/530, 307/352, 307/481, 370/85.1
• US Class Current: 375/257
• CPC Class Codes: G06F 13/4072 Drivers or receivers G06F13/4086 takes precedence; for multistate logic circuits H03K19/0002
• CPC Class Codes: H03K 3/356043 with synchronous operation
• CPC Class Codes: H04L 25/0282 Provision for current-mode coupling
• CPC Class Codes: H04L 25/0298 Arrangement for terminating transmission lines
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

In the high speed bus system of the present invention, the bus configuration is one in which all master devices are clustered at one end of an unterminated end of the bus. The slaves are located along the remaining length of the bus and the opposite end of the transmission line of the bus is terminated. By eliminating the termination resistor at the end of the bus where the master devices are located the required drive current needed to produce a given output swing is reduced. The bus drivers and receivers are CMOS integrated circuits. The bus of the present invention is operable utilizing small swing signals which enable sufficient implementation of current mode drivers for low impedance bus signals. In particular, the bus input receiver of the present invention comprises a two stage buffered sampler/amplifier which receives a small swing signal from the bus and samples and amplifies the low swing signal to a full swing signal within a single clock cycle using CMOS circuits.

Claims

1. A high speed bus system for coupling at least one master device to at least one slave device, said bus comprising at least one transmission line for transmission of signals, said master device and said slave device coupled to the transmission line;

each master device and slave device comprising a bus driver and bus receiver;

said bus driver comprising a current mode source to drive current along the transmission line,

said bus receiver comprising at least one sampler/amplifier circuits which sample the received signal and amplify the signal from a small swing voltage level to a large swing voltage level compatible with the device coupled to the receiver, each of said sampler/amplifier circuits comprising,

a first stage sampler circuit for sampling the received signal,

a second stage amplifier circuit for amplifying the received signal to a voltage level compatible with the device coupled to the receiver, said second stage electrically isolated from the first stage, and

means for transferring the sampled received signal from the first stage to the second stage;

whereby the parasitic capacitive charge that is back injected onto the transmission line by the first stage sampler circuit is minimized by maintaining a small swing signal at the first stage and transferring the sampled small swing signal to the isolated second stage prior to amplifying the small swing signal to a large swing signal and the signal received by the bus receiver is output rapidly in a form compatible with the device coupled to the bus receiver.

2. The high speed bus system as set forth in claim 1, wherein said receiver circuit comprises a first and second sampler/amplifier circuit, said first sampler/amplifier circuit operating on a first edge of the clock and said second sampler/amplifier operating on a second edge of the clock.

3. The high speed bus system as set forth in claim 1, wherein said small swing signal comprises a swing of approximately 500 millivolts wherein V_OL approximately equals 2.0 volts and V_OH approximately equals 2.5 volts.

4. The high speed bus system as set forth in claim 1, wherein said receiver circuit comprises CMOS circuitry.

5. The high speed bus system as set forth in claim 4, wherein said small swing signal comprises a swing of approximately 500 millivolts wherein V_OL approximately equals 2.0 volts and V_OH approximately equals 2.5 volts and said large swing signal comprises a swing of approximately 5 volts wherein V_OL approximately equals 0.0 volts and V_OH is in the range of approximately 3.3 to 5.0 volts.

6. The high speed bus system as set forth in claim 1, wherein said first stage sampler circuit comprises a differential amplifier having a gain close to unity.

7. The high speed bus system as set forth in claim 1, wherein said second stage amplifier circuit comprises a sense amplifier.

8. The high speed bus system as set forth in claim 1, wherein said first stage sampler circuit is isolated from said second stage amplifier circuit by isolation transistors, said isolation transistors, when in an off state, isolate the first stage sampler circuit from the second stage amplifier circuit.

9. The high speed bus system as set forth in claim 8, wherein said means for transferring the sampled received signal from the first stage to the second stage comprises said isolation transistors in an on state.

10. The high speed bus system as set forth in claim 9, wherein the bus driver comprises an NMOS transistor operating as a constant current source.

23. The high speed bus system as set forth in claim 1 wherein each of the sampler/amplifier circuits operating on alternate clocks to increase the throughput of the receiver.

11. A high speed bus system for coupling at least one master device to at least one slave device, said bus comprising at least one low impedance transmission line for transmission of signals, said master device and said slave device coupled to the at least one transmission line;

each master device and slave device comprising at least a bus driver and bus receiver;

said bus driver comprising current mode source to drive current along the transmission line at a low, small swing voltage,

said bus receiver comprising a plurality of sampler/amplifier circuits which sample the received signal and amplify the signal from the small swing voltage level to a large swing voltage level compatible with the device coupled to the receiver, each of said sampler/amplifier circuits operating on alternate clocks to increase the throughput of the receiver, each of said sampler/amplifier circuits comprising,

a first stage circuit for sampling the received signal, said first stage comprising a differential amplifier having a gain close to unity,

a second stage circuit comprising a sense amplifier for amplifying the received signal to a voltage level compatible with the device coupled to the receiver, said second stage electrically isolated from the first stage, and

means for transferring the sampled received signal from the first stage to the second stage;

whereby the parasitic capacitive charge that is back injected onto the transmission line by the first stage circuit is minimized by maintaining a small swing signal at the first stage and transferring the sampled small swing signal to the isolated second stage prior to amplifying the small swing signal to a large swing signal and the signal received by the bus receiver is output rapidly in a form compatible with the device coupled to the bus receiver.

12. The high speed bus system as set forth in claim 11, wherein said small swing signal comprises a swing of approximately 500 millivolts wherein V_OL approximately equals 2.0 volts and V_OH approximately equals 2.5 volts.

13. The high speed bus system as set forth in claim 11, wherein said receiver circuit comprises CMOS circuitry.

14. The high speed bus system as set forth in claim 11, wherein said first stage sampler circuit is isolated from said second stage amplifier circuit by isolation transistors, said isolation transistors, when in an off state, isolate the first stage sampler circuit from the second stage amplifier circuit.

15. The high speed bus system as set forth in claim 14, wherein said means for transferring the sampled received signal from the first stage to the second stage comprises said isolation transistors in an on state.

16. In a high speed bus system for coupling at least one master device to at least one slave device, said bus comprising at least one transmission line for transmission of signals, said master device and said slave device coupled to the at least one transmission line a method for transmitting signals between a transmitting device and a receiving device of the master and slave devices, said method comprising the steps of:

driving a signal on the bus utilizing a current mode source to drive current along the transmission line at a small swing voltage;

sampling the signal at a first stage of the receiver device;

transferring the sampled signal to a second stage of the receiver device, said second stage electrically isolated from the first stage;

amplifying the sampled received signal from the small swing voltage to a large swing voltage level compatible with a device coupled to the receiver;

whereby parasitic capacitive charge that is back injected onto the transmission line by the first stage circuit is minimized by maintaining a small swing signal at the first stage and transferring the sampled small swing signal to the isolated second stage prior to amplifying the small swing signal to a large swing signal and the signal received by the bus receiver is output rapidly in a form compatible with the device coupled to the bus receiver.

17. The method as set forth in claim 16, wherein said small swing signal comprises a swing of approximately 500 millivolts wherein V_OL approximately equals 2.0 volts and V_OH approximately equals 2.5 volts.

18. A high speed bus configuration for coupling at least one master device to at least one slave device, said bus comprising:

at least one transmission line, said master device coupled to a first end of the transmission line, said slave device coupled to the transmission line at a point between the first end and a second end of the transmission line;

a termination resistor located at the second end of the transmission line, said resistor having an impedance equivalent to the impedance of the transmission line whereby signals which travel to the second end of the transmission line are absorbed;

said slave device communicating to the master device by producing a drive current which is divided at the output of the slave device to generate first and second 1/2 swing signals, the first 1/2 swing signal propagating towards the second end of the transmission line and said second 1/2 swing signal propagating towards the first end of the transmission line;

said terminating resistor absorbing the first 1/2 swing signal, said second 1/2 swing signal reaching the first end of the transmission line and reflecting back towards the second end of the bus, said master devices located at the first end of the bus receiving a full swing signal resulting from the sum of the first 1/2 swing signal and reflected first 1/2 swing signal;

whereby the power dissipation along the bus is minimized without increasing the time of flight delay (t_f) of the bus and the effectiveness of the master and slave devices as bus drivers is increased.

19. The high speed bus configuration as set forth in claim 18, wherein bus drivers of the master and slave devices are current drivers and present a high impedance to the bus, whereby signals transmitted to drivers continue to propagate down the bus without secondary reflections caused by low impedance drivers.

20. The high speed bus configuration as set forth in claim 18, wherein bus receivers of the master and slave devices comprise a plurality of sampler/amplifier circuits which sample the received signal and amplify the signal from a small swing voltage level to a large swing voltage level compatible with the device coupled to the receiver, each of said sampler/amplifier circuits operating on alternate clocks to increase the throughput of the receiver, each of said sampler/amplifier circuits comprising,

a first stage sampler circuit for sampling the received signal,

a second stage amplifier circuit for amplifying the received signal to a voltage level compatible with the device coupled to the receiver, said second stage electrically isolated from the first stage, and

means for transferring the sampled received signal from the first stage to the second stage;

whereby the parasitic capacitive charge that is back injected onto the transmission line by the first stage sampler circuit is minimized by maintaining a small swing signal at the first stage and transferring the sampled small swing signal to the isolated second stage prior to amplifying the small swing signal to a large swing signal and the signal received by the bus receiver is output rapidly in a form compatible with the device coupled to the bus receiver.

21. The high speed bus configuration as set forth in claim 18, wherein bus drivers of the master and slave devices are current drivers and transmit a small swing signal comprising a swing of approximately 500 millivolts wherein V_OL approximately equals 2.0 volts and V_OH approximately equals 2.5 volts.

22. The high speed bus configuration as set forth in claim 18, wherein said master devices communicates with the slave device by driving a full swing signal which propagates from the master device at the first end of the transmission line towards the slave device and the second end of the transmission line.