Folding non linear pipeline ADC Investigation

Prof. Joerg Vollrath, 16.12.2020

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Transfer Characteristic

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Simulation

Bit loss 10-bit linear pipeline ADC with gain error


GainCodesMaximum CodeENOB (Number of Code based)
2.0 1023102310.00
1.95 87510009.77
1.9 7359789.52
1.85 6299629.30
1.8 5259389.04

8-bit non linear


ADC Simulation tool

Residue function
Transfer function

INLDNL function
FFT function
Summary:
INLmax= 30
SNR = -10.96 dB - (-29.79 dB)) = 18.83 dB
ENOB = 3 Bit

Select ramp data and process with FFT tool with calibration

No code calibration:
SNR = 34.2 dB - 15.37 dB = 18.83 dB
Code calibration:
202 codes
Sine data:
SNR = 33.63 dB - 8.72 dB = 34.99 dB
Code and slope calibration:
128 unique codes.
SNR = 30.06 - (-11.99) = 42.05 dB

FFT function after code and slope calibration

10-bit non linear

ADC Simulation

Residue function
Transfer function

INLDNL function
FFT function
Summary:
INLmax= 110
SNR = -10.89 dB - (-29.42 dB)) = 18.53 dB
ENOB = 3 Bit



SNR = 42.13 dB - (-11.6 dB) = 53.73 dB
ENOB = 8.5 dB

10-bit non linear

ADC Simulation
Offset 0.05
Gain1 1.8
Gain2 1.9


Residue function
Transfer function

INLDNL function
FFT function
SNR = -11.52 dB - (-30.36 dB) = 18.16 dB

Code and slope calibration gives 29 unique codes.
SNR = 16.79 dB - (-12.72 dB)) = 29.51 dB


Summary


A non linear residue function reduces the SNR for a 8-bit and-10 bit folding pipeline ADC from expected 50 dB to 18.83 dB (ENOB=3).

Code and slope calibration improves the performance increasing SNR for 8-bits to 35 (ENOB=6, code) and 42 dB (ENOB=7, code and slope) and for a 10-bit ADC to 53.73 dB (ENOB=8.5, code and slope).

Even a non-linear residue function with offset (0.05) and gain error (1.8,1.9) gives for 10-bit folding pipeline ADC (114 unique codes) 18.16 dB (ENOB=3).
Calibration gives only 28 unique codes and improves this to 29.51 dB (ENOB = 4.5).