A Fill-In Technique for Robust IMD Suppression in Chopper Amplifiers
C.T. Rooijers (TU Delft - Electronic Instrumentation)
S. Karmakar (TU Delft - Electronic Instrumentation)
Y. Kusuda (Analog Devices)
JH Huijsing (TU Delft - Electronic Instrumentation)
K. A.A. Makinwa (TU Delft - Microelectronics)
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Abstract
In chopper amplifiers, the interaction between the input signal and the chopper clock can give rise to intermodulation distortion (IMD). This chopper-induced IMD is mainly due to amplifier delay, which causes large pulses at the output of the amplifier's output chopper. This article proposes the use of a so-called fill-in technique to eliminate these pulses, and thus the resulting IMD, by multiplexing the outputs of two identical amplifiers that are chopped in quadrature. A prototype chopper-stabilized amplifier was implemented in a 180-nm CMOS process. Measurements show that the fill-in technique suppresses chopper-induced IMD by 28 dB, resulting in an IMD of -126 dB for input frequencies near 4 FCH (=80 kHz). It also improves the amplifier's two-tone IMD (with 79 and 80 kHz inputs) from -97 to -107 dB, which is the same as that obtained without chopping.