US 8,427,198 B1Granted

Reduced quantization error I/O resistor calibrator

AssigneeArm Limited

InventorsSridhar Cheruku, Sivaramakrishnan Subramanian, Nidhir Kumar

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Abstract

Calibration circuitry 42 for an off-chip driver circuit 4 and/or an on-die termination circuit 8 is provided using a parallel network of main transistors controlled by a N-bit calibration value. During the calibration operation, the N-bit calibration value is varied until a threshold impedance value is crossed by the combination of the main transistors. A rounding transistor 52 is then used to determine which of the N-bit calibration values produces a combined impedance closest to the designed threshold impedance.

Claims22

Dependent claims

A method of calibrating an impedance for a data transfer circuit using a calibration circuit having a plurality of main transistors respectively switched between a high impedance state and a low impedance state by a respective bit value signal of an N-bit calibration value, said plurality of main transistors being arranged in parallel with each other and a rounding transistor to provide a combined impedance, said method comprising the steps of:

(a) setting a default value for an impedance of said rounding transistor and a current N-bit calibration value to a first value in a sequence of N-bit calibration values corresponding to a monotonically changing combined impedance;
(b) detecting if said combined impedance has crossed a threshold value and one of:
(i) if said combined impedance has not crossed said threshold impedance, then setting said current N-bit calibration value to a next value in said sequence and repeating step (b);
and
(ii) if said combined impedance has crossed said threshold value, then:
(1) selecting a value for said N-bit calibration value and changing said impedance of said rounding transistor from said default value to a changed value to provide a further combined impedance with a magnitude between said combined impedance that crossed said threshold value and a preceding impedance value that did not cross said threshold value;
(2) detecting if said further combined impedance value remains as crossed said threshold value and one of:
(A) if said further combined impedance remains as crossed said threshold value, then setting as a determined N-bit calibration value that value of said calibration N-bit value corresponding to said preceding combined impedance that did not cross said threshold value;
and
(B) if said further combined impedance does not remains as crossed said threshold value, then setting as a determined N-bit calibration value that value of said calibration N-bit value corresponding to said combined impedance that did cross said threshold value.

7 more elements

An integrated circuit having a data transfer circuit calibrated using a calibration circuit, said calibration circuit comprising:

a plurality of main transistors and a rounding transistor, said plurality of main transistor respectively switched between a high impedance state and a low impedance state by a respective bit value signal of an N-bit calibration value, said plurality of main transistors being arranged in parallel with each other and said rounding transistor to provide a combined impedance;
and
calibration control circuitry configured to generate said N-bit calibration value, to control impedance of said rounding transistor and to control said calibration circuit to operate:
(a) to set a default value for an impedance of said rounding transistor and a current N-bit calibration value to a first value in a sequence of N-bit calibration values corresponding to a monotonically changing combined impedance;
(b) to detect if said combined impedance has crossed a threshold value and one of:
(i) if said combined impedance has not crossed said threshold impedance, then to set said current N-bit calibration value to a next value in said sequence and to repeat (b);
and
(ii) if said combined impedance has crossed said threshold value, then:
(1) to select a value for said N-bit calibration value and to change said impedance of said rounding transistor from said default value to a changed value to provide a further combined impedance with a magnitude between said combined impedance that crossed said threshold value and a preceding impedance value that did not cross said threshold value;
(2) to detect if said further combined impedance value remains as crossed said threshold value and one of:
(A) if said further combined impedance remains as crossed said threshold value, then to set as a determined N-bit calibration value that value of said calibration N-bit value corresponding to said preceding combined impedance that did not cross said threshold value;
and
(B) if said further combined impedance does not remains as crossed said threshold value, then to set as a determined N-bit calibration value that value of said calibration N-bit value corresponding to said combined impedance that did cross said threshold value.

10 more elements

An integrated circuit having a data transfer circuit calibrated using a calibration circuit, said calibration circuit comprising:

a plurality of main transistors and a rounding transistor, said plurality of main transistor respectively switched between a high impedance state and a low impedance state by a respective bit value signal of an N-bit calibration value, said plurality of main transistors being arranged in parallel with each other and said rounding transistor to provide a combined impedance;
and
calibration control means for generating said N-bit calibration value, for controlling impedance of said rounding transistor and for controlling said calibration circuit to operate:
(a) to set a default value for an impedance of said rounding transistor and a current N-bit calibration value to a first value in a sequence of N-bit calibration values corresponding to a monotonically changing combined impedance;
(b) to detect if said combined impedance has crossed a threshold value and one of:
(i) if said combined impedance has not crossed said threshold impedance, then to set said current N-bit calibration value to a next value in said sequence and to repeat (b);
and
(ii) if said combined impedance has crossed said threshold value, then:
(1) to select a value for said N-bit calibration value and to change said impedance of said rounding transistor from said default value to a changed value to provide a further combined impedance with a magnitude between said combined impedance that crossed said threshold value and a preceding impedance value that did not cross said threshold value;
(2) to detect if said further combined impedance value remains as crossed said threshold value and one of:
(A) if said further combined impedance remains as crossed said threshold value, then to set as a determined N-bit calibration value that value of said calibration N-bit value corresponding to said preceding combined impedance that did not cross said threshold value;
and
(B) if said further combined impedance does not remains as crossed said threshold value, then to set as a determined N-bit calibration value that value of said calibration N-bit value corresponding to said combined impedance that did cross said threshold value.

10 more elements

Dependencies are inferred from the claim text.

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Abstract

(a) setting a default value for an impedance of said rounding transistor and a current N-bit calibration value to a first value in a sequence of N-bit calibration values corresponding to a monotonically changing combined impedance;
(b) detecting if said combined impedance has crossed a threshold value and one of:
(i) if said combined impedance has not crossed said threshold impedance, then setting said current N-bit calibration value to a next value in said sequence and repeating step (b);
and
(ii) if said combined impedance has crossed said threshold value, then:
(1) selecting a value for said N-bit calibration value and changing said impedance of said rounding transistor from said default value to a changed value to provide a further combined impedance with a magnitude between said combined impedance that crossed said threshold value and a preceding impedance value that did not cross said threshold value;
(2) detecting if said further combined impedance value remains as crossed said threshold value and one of:
(A) if said further combined impedance remains as crossed said threshold value, then setting as a determined N-bit calibration value that value of said calibration N-bit value corresponding to said preceding combined impedance that did not cross said threshold value;
and
(B) if said further combined impedance does not remains as crossed said threshold value, then setting as a determined N-bit calibration value that value of said calibration N-bit value corresponding to said combined impedance that did cross said threshold value.

7 more elements