Circuit and method for cascading programmable impedance matching in a multi-chip system

1. A programmable impedance matching circuit, comprising:

a plurality of chips arranged in a cascading configuration,

wherein a cascade output pin of a chip is coupled to a cascade input pin of a cascade chip to enable handshaking between the plurality of chips,

wherein the plurality of chips are coupled to a common precision resistor via a common impedance line to enable each chip to calibrate an impedance of the chip, and

wherein each of the plurality of chips comprises:

a control circuit,

wherein the control circuit includes a state machine circuit, and

wherein the control circuit is configured to control a non-overlapping clock cycle of each chip during which the impedance of the chip is evaluated.

2. The circuit of claim 1 , wherein the plurality of chips are arranged in a master and slave configuration.

3. The circuit of claim 1 , wherein each control circuit comprises:

a pull up driver and a pull down driver, and

wherein the state machine circuit is coupled to both the pull up and the pull down drivers of the control circuit.

4. The circuit of claim 1 , wherein the plurality of chips comprises at least one of dual data rate (DDR) memory chips and quad data rate (QDR) memory chips.

5. The circuit of claim 2 , wherein the master chip of the plurality of chips is configured to receive a ground level signal, and

wherein the control circuit of each ship is configured to regulate output impedance.

6. The circuit of claim 1 , wherein the control circuit of each chip is configured to control the corresponding state machine to operate each chip with a gap of n clock cycles from one another, and

wherein n comprises an integer.

7. The circuit of claim 1 , wherein a non-overlapping impedance evaluation is performed to control circuit on each of the plurality of chips,

wherein a gap of n clock cycles is maintained between cascaded chips, and

wherein n comprises a numerical value.

8. A system for programmable impedance matching, comprising:

a plurality of chips arranged in a cascaded configuration, each comprising a cascade input pin and a cascade output pin,

wherein the plurality of cascaded chips is coupled to a common precision resistor, and

wherein each of the plurality of cascaded chips comprises:

an impedance controlling state machine,

wherein each impedance controlling state machine is configured to operate during a non-overlapping clock cycle, and

wherein the system is configured to regulate output driver impedance for the multi-chip cascaded configuration.

9. The system of claim 8 , wherein the system is configured to provide compensation for process, voltage and temperature (PVT) variations between the plurality of cascaded chips.

10. The system of claim 8 , wherein the plurality of cascaded chips comprises a plurality of static random access memory (SRAM) chips.

11. The system of claim 10 , wherein the plurality of SRAM chips further comprise dual data rate (DDR) memory chips or quad data rate (QDR) memory chips.

12. The system of claim 8 , comprising:

a control circuit in communication with the plurality of cascaded chips,

wherein the control circuit is configured to perform a pull up and pull down impedance evaluation in each of the plurality of chips.

13. The system of claim 8 , wherein one of the plurality of cascaded chips is configured as a master chip, and

wherein remaining ones of the plurality of cascaded chips are configured as slave chips.

14. A method of programmable impedance matching in a plurality of cascaded chips comprising:

resetting a control state machine in each of the plurality of cascaded chips after a power-up signal,

wherein the control state machines are reset during a first period of non-overlapping clock cycles; and

performing an impedance evaluation for each of the plurality of cascaded chips during a second period of non-overlapping clock cycles.

15. The method of claim 14 , wherein the non-overlapping clock cycles are each of length n, and

wherein n comprises an integer.

16. The method of claim 14 , wherein the step of performing comprises:

terminating a common impedance line of the plurality of cascaded chips with a common precision resistor.

17. The method of claim 14 , wherein the step of performing comprises:

turning on a pull up replica for each of the plurality of cascaded chips.

18. The method of claim 17 , wherein the step of turning on comprises:

evaluating a pull up replica for a master chip during a first clock cycle; and

evaluating pull up replicas for a plurality of slave chips during a plurality of clock cycles occurring after the first clock cycle,

wherein both the first clock cycle and each of the plurality of clock cycles are non-overlapping.