Anti-noise input/output impedance control of semiconductor circuit with reduced circuit size

1. An impedance control system comprising:

a target circuit having a controllable impedance;

a replica circuit having a structure identical to said target circuit;

a first binary counter providing said replica circuit with a first impedance control code indicative of a counter value of said first binary counter, wherein an impedance of said replica circuit is controlled in response to said first impedance control code;

a comparator comparing a voltage received from said replica circuit with a reference signal;

a second binary counter responsive to an output signal from said comparator for counting a number of times when said output signal is set to a predetermined state; and

a control circuit extracting upper multiple bits out of a counter value of said second binary counter, and generating a second impedance control code indicative of said upper multiple bits,

wherein said impedance of said target circuit is controlled in response to said second impedance control code.

2. The impedance control system according to claim 1 , wherein said counter value of said first binary counter consists of n bits, and said counter value of said second binary counter consists of n+k bits, where n is an integer equal to or more than three, and k is an integer equal to or more than one.

3. The impedance control system according to claim 2 , wherein said control circuit is configured to control said first binary counter so that said first binary counter is scanned 2 k times from all “0” to all “1”, or from all “1” to all “0”, and to generates said second impedance control code so as to indicate of upper n bits of said counter value of said second binary counter.

4. The impedance control system according to claim 1 , wherein said control circuit is configured to control said first binary counter so that said first binary counter is counted up from all “0” to all “1” during a first scanning of said first binary counter, and counted down from all “1” to all “0” during a second scanning of said first binary counter following said first scanning.

5. An impedance control circuit comprising:

a first binary counter providing a replica circuit of a target circuit having a controllable impedance a first impedance control code indicative of a counter value of said first binary counter, for controlling an impedance of said replica circuit;

a second binary counter responsive to an output signal from a comparator comparing a voltage received from said replica circuit with a reference signal for counting a number of times when said output signal is set to a predetermined state; and

a control circuit extracting upper multiple bits out of a counter value of said second binary counter, and generating a second impedance control code indicative of said upper multiple bits for controlling an impedance of said target circuit.

6. The impedance control circuit according to claim 5 , wherein said counter value of said first binary counter consists of n bits, and said counter value of said second binary counter consists of n+k bits, where n is an integer equal to or more than three, and k is an integer equal to or more than one.

7. The impedance control circuit according to claim 6 , wherein said control circuit is configured to control said first binary counter so that said first binary counter is scanned 2 k times from all “0” to all “1”, or from all “1” to all “0”, and to generates said second impedance control code so as to indicate upper n bits of said counter value of said second binary counter.

8. The impedance control circuit according to claim 5 , wherein said control circuit is configured to control said first binary counter so that said first binary counter is counted up from all “0” to all “1” during a first scanning of said first binary counter, and counted down from all “1” to all “0” during a second scanning of said first binary counter following said first scanning.

9. A semiconductor device comprising:

a target circuit having a controllable impedance;

a replica circuit having a structure identical to said target circuit;

a first binary counter providing said replica circuit with a first impedance control code indicative of a counter value of said first binary counter, wherein an impedance of said replica circuit is controlled in response to said first impedance control code;

a comparator comparing a voltage received from said replica circuit with a reference signal;

a second binary counter responsive to an output signal from said comparator counting a number of times when said output signal is set to a predetermined state; and

a control circuit extracting upper multiple bits out of a counter value of said second binary counter, and generating a second impedance control code indicative of said upper multiple bits,

wherein said impedance of said target circuit is controlled in response to said second impedance control code, and

wherein said target circuit, said replica circuit, said first binary counter, said second binary counter, and said control circuit are monolithically integrated within a semiconductor chip.

10. A SerDes driver circuitry comprising:

a SerDes driver having a controllable output impedance;

a replica circuit having a structure identical to said SerDes driver;

a first binary counter providing said replica circuit with a first impedance control code indicative of a counter value of said first binary counter, wherein an output impedance of said replica circuit is controlled in response to said first impedance control code;

a comparator comparing a voltage received from said replica circuit with a reference signal;

a second binary counter responsive to an output signal from said comparator for counting a number of times when said output signal is set to a predetermined state; and

a control circuit extracting upper multiple bits out of a counter value of said second binary counter, and generating a second impedance control code indicative of said upper multiple bits,

wherein said output impedance of said SerDes driver is controlled in response to said second impedance control code.

11. A SerDes receiver circuitry comprising;

a SerDes receiver having a controllable input impedance;

a replica circuit having a structure identical to said SerDes receiver;

a first binary counter providing said replica circuit with a first impedance control code indicative of a counter value of said first binary counter, wherein an input impedance of said replica circuit is controlled in response to said first impedance control code;

a comparator comparing a voltage received from said replica circuit with a reference signal;

a second binary counter responsive to an output signal from said comparator for counting a number of times when said output signal is set to a predetermined state; and

a control circuit extracting upper multiple bits out of a counter value of said second binary counter, and generating a second impedance control code indicative of said upper multiple bits,

wherein said input impedance of said SerDes receiver is controlled in response to said second impedance control code.

12. A method of controlling an impedance of a target circuit, comprising:

scanning a counter value of a first binary counter between all “0” and all “1” to generate a first impedance control code;

controlling an impedance of a replica circuit having a structure identical to said target circuit;

comparing a voltage received from said replica circuit with a reference signal by a comparator to generate an output signal;

counting up or down a second binary counter in response to said output signal;

extracting upper multiple bits out of a counter value of said second binary counter to generate a second impedance control code indicative of said upper multiple bits; and

controlling said impedance of said target circuit in response to said second impedance control code.

13. The method according to claim 12 , wherein said counter value of said first binary counter consists of n bits, and said counter value of said second binary counter consists of n+k bits, where n is an integer equal to or more than three, and k is an integer equal to or more than one.

14. The method according to claim 13 , wherein said scanning of said counter value of said first binary counter is repeated 2 k times every when a value of said second impedance control code is determined.

15. The method according to claim 12 , wherein said scanning includes:

counting up said first binary counter from all “0” to all “1”; and

counting down said first binary counter from all “1” to all “0”, and

wherein said counting up and counting down are alternately performed.