Amplifiers often employ chopping to achieve low offset and low-frequency noise. However, the interaction between the input signal and the chopper clock can cause chopper-induced intermodulation distortion (IMD)  -. This is especially problematic for input frequencies (Fin) near even multiples of the chopping frequency (FCH), as the resulting IMD tones fold-back to low frequencies and so cannot be filtered out. In  -, spread-spectrum clocks are used to convert such tones into noise-like signals. However, this increases the noise floor and does not address the underlying problem. This paper shows that chopper-induced IMD is mainly due to amplifier delay, which results in large chopping spikes. A novel fill-in technique is proposed that mitigates these spikes, and so reduces the chopper-induced IMD. In a prototype chopper-stabilized amplifier, it reduces the chopper-induced IMD by 28dB, resulting in an IMD of -126dB for input frequencies near 4FCH (=80kHz). Similarly, it improves the chopped amplifier's two-tone IMD (79 and 80kHz) from -97dB to -107dB, thus maintaining the same IMD as the un-chopped amplifier.
|Title of host publication||2021 IEEE International Solid-State Circuits Conference, ISSCC 2021 - Digest of Technical Papers|
|Publisher||Institute of Electrical and Electronics Engineers (IEEE)|
|Number of pages||3|
|Publication status||Published - 2021|
|Event||2021 IEEE International Solid-State Circuits Conference, ISSCC 2021 - San Francisco, United States|
Duration: 13 Feb 2021 → 22 Feb 2021
|Name||Digest of Technical Papers - IEEE International Solid-State Circuits Conference|
|Conference||2021 IEEE International Solid-State Circuits Conference, ISSCC 2021|
|Period||13/02/21 → 22/02/21|
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