Output buffer circuit with control circuit for modifying supply voltage and transistor size
First Claim
1. A semiconductor integrated circuit comprising in a semiconductor chip:
- an internal circuit;
an external output buffer connected to the internal circuit; and
a control circuit capable of requesting to modify an operational supply voltage given to the external output buffer, and capable of selectively controlling an output transistor size of the external output buffer according to the operational supply voltage, wherein the control circuit determines by using a dummy circuit an impedance matching state of the external output buffer and a transmission line connected outside the chip to the external output buffer, and selectively controls the output transistor size according to an external power supply voltage.
4 Assignments
0 Petitions
Accused Products
Abstract
In this invention, a control circuit (111) controls both the power supply voltage (VDDQ) and the transistor size of the external output buffer to thereby select the lowest supply voltage that achieves the impedance matching with the transmission line (100), to thereby save bus termination by a resistor, thus consequently achieving both the lowering of the power consumption and the speeding-up in the data transmission. The power consumption during the data transmission is proportional to the square of the supply voltage. If the operational supply voltage of the external output buffer is lowered, the power consumption will be reduced accordingly. If the operational supply voltage of the external output buffer is lowered, the impedance thereof will be increased apparently; and at the same time, if the transistor size of the external output buffer is increased, the increased impedance will be decreased. By bringing the output impedance (ON-resistance) of the external output buffer into conformity with the impedance of the transmission line, it becomes possible to output the signal without distortions on the waveform.
10 Citations
16 Claims
-
1. A semiconductor integrated circuit comprising in a semiconductor chip:
-
an internal circuit;
an external output buffer connected to the internal circuit; and
a control circuit capable of requesting to modify an operational supply voltage given to the external output buffer, and capable of selectively controlling an output transistor size of the external output buffer according to the operational supply voltage, wherein the control circuit determines by using a dummy circuit an impedance matching state of the external output buffer and a transmission line connected outside the chip to the external output buffer, and selectively controls the output transistor size according to an external power supply voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 12)
-
-
10. A semiconductor integrated circuit comprising in a semiconductor chip:
-
an internal circuit;
an external output buffer connected to the internal circuit; and
a control circuit capable of requesting to modify an operational supply voltage given to the external output buffer, and capable of selectively controlling an output transistor size of the external output buffer according to the operational supply voltage, wherein the control circuit selectively controls the output transistor size according to an external power supply voltage, in a direction of making an impedance matching of the external output buffer and a transmission line connected outside the chip to the external output buffer, and wherein the control circuit outputs first information to designate a level of the operational supply voltage, and selectively controls the output transistor size according to the operational supply voltage answered in response to the first information; and
when it is impossible to select the output transistor size for making the impedance matching, the control circuit requests to modify the operational supply voltage by means of the first information to redo selecting the output transistor size. - View Dependent Claims (11, 13, 14, 15)
-
-
16. A semiconductor integrated circuit comprising in a semiconductor chip:
-
an internal circuit;
an external output buffer connected to the internal circuit; and
a control circuit capable of requesting to modify an operational supply voltage given to the external output buffer, and capable of selectively controlling an output transistor size of the external output buffer according to the operational supply voltage, wherein the control circuit selectively controls the output transistor size according to an external power supply voltage, in a direction of making an impedance matching of the external output buffer and a transmission line connected outside the chip to the external output buffer, and wherein the control circuit receives second information from the outside, starts the selective control of the output transistor size according to the operational supply voltage by responding to the second information, outputs third information to the outside when it is impossible to select an output transistor size for making the impedance matching, and outputs fourth information to the outside when it is possible to select the output transistor size for making the impedance matching.
-
Specification