The circuit uses the LTC1043 in a variable gain amplifier which features continuously variable gain, gain stability of 20 PPM/degree C, and single-ended or differential inputs. The circuit uses two separate LTC1043s. LTC1043B is continuously clocked by a 1-kHz source, which could also be processor supplied.
Both LTC1043s function as the sampled data equivalent of a resistor within the bandwidth set by A1's 0.01-uF value and the switched-capacitor equivalent feedback resistor. The time-averaged current delivered to the summing point by LTC1043A is a function of the 0.01uF capacitor's input-derived voltage and the commutation frequency at pin 16. Low-commutation frequencies result in small time-averaged current values, and require a large impute resistor. Higher frequencies require an equivalent small input resistor.