Noise Reduction in High Resolution ADC

The pipelined successive approximation analog to digital converter is widely used to implement the Nyquist ADC with the resolution higher than 16 bits. Its residual amplifier can contribute a significant portion of ADC total noise. The paper proposes and analyzes a noise reduction technique which is based on the auto zero method. It can be used in a closed-loop amplifier with a resistor-feedback network to reduce low-frequency noise, especially 1/f noise. The amplifier inputs are shorted to amplify its own noise which is saved in 2nd stage DAC. The saved noise would be subtracted from the amplified residual signal to remove low-frequency noises. The method is verified by an 18-bit SA-ADC in a 180-nm CMOS ADC. Simulation results show that the in-band noise contribution from the residual amplifier in the ADC output is reduced by about 40%.