MCP6V71 - Why are there peaks at 1 kHz and 2 kHz in Figure 2-41 of the datasheet?
  • Peaks at 1 kHz: The datasheet states that this is due to a resistor mismatch. If the application is a difference amplifier and the resistors are chosen properly, then the resistors set a CMRR to about: CMRR_R = 20 log(GDM 4 / TOLR). For example, using the conditions shown in these plots, 0.1% resistors setting a differential gain of 10 V/V, limits the CMRR to about 92 dB. This would give a residual tone of about 2.5 µVPK at 1 kHz.
  • Peaks at 2 kHz and above: The tones at 2 kHz and above are the results of non-linear distortion (IMD) due to the interaction between the internal chip clock and the external sine wave at 1 kHz. These tones do not exist without the externally applied signal. The distortion tone at 2 kHz in Fig. 2-41 (rev. B of the datasheet) is about -106 dBc; this is good enough for the majority of applications. Changing the conditions will change this specific number.
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