SAR ADC and method with INL compensation

1. An apparatus comprising:

a capacitive digital-to-analog converter (CDAC) that receives an analog input signal;

a successive approximation register (SAR) controller that is coupled to the CDAC and that provides a digital code representing a conversion result; and

an integral non-linearity (INL) compensator is coupled to the SAR controller so as to receive the digital code and that is coupled to the CDAC so as to provides an INL compensation signal to the CDAC to reduce an INL in response to the digital code.

2. The apparatus of claim 1 , wherein the INL compensation signal is an analog signal.

3. The apparatus of claim 1 , wherein the CDAC further comprises:

a first set of capacitors that receive in the analog input signal; and

a compensation capacitor coupled to receive the INL compensation signal.

4. The apparatus of claim 1 , wherein the INL compensator further comprises:

a reference signal generator;

an INL digital-to-analog converter (DAC) that is coupled to the reference signal generator; and

an interpolation amplifier that is coupled to the INL DAC and to the CDAC.

5. The apparatus of claim 4 , wherein the INL DAC further comprises:

a processor that is coupled to the SAR controller;

a switched resistor network that is coupled the reference signal generator and that is controlled by the processor; and

an operational amplifier that is coupled to the resistor network and the interpolation amplifier.

6. The apparatus of claim 4 , wherein the reference signal generator further comprises:

a first current source;

a second current source;

a current mirror that is coupled to the first and second current sources;

an operational amplifier that is coupled to the first and second current sources;

a first bipolar transistor that is coupled to the current mirror, wherein the first bipolar transistor is diode-connected;

a second bipolar transistor that is coupled between the first diode-connected transistor and ground, wherein the second bipolar transistor is diode-connected;

a third bipolar transistor that is coupled to the current mirror at its collector and the operational amplifier at its emitter, wherein the third bipolar transistor is diode-connected; and

a fourth bipolar transistor that is coupled to the emitter of the third bipolar transistor at its base and that is coupled to the INL DAC circuit at its collector.

7. The apparatus of claim 4 , wherein the interpolating amplifier further comprises:

a switch controller that is coupled to the SAR controller;

a switched resistor network that is controlled by the switch controller; and

a plurality of differential amplifiers that are each coupled to the switched resistor network; and

an operational amplifier that is coupled to each differential amplifier and the CDAC.