US Patent 8072262 Low input bias current chopping switch circuit and method

A chopper-stabilized circuit (1) includes pre-chopping circuitry (26) for chopping an input signal (Vin) at a first frequency to generate a first signal. Input chopping circuitry (9) chops the first signal at a second frequency substantially greater than the first frequency to produce a second signal. The first frequency is a sub-harmonic of the second frequency. Post-chopping circuitry (30) chops the second chopped signal at the first frequency to produce a third signal that is applied to an input of a signal conditioning circuit (2). The output chopping circuitry (10) chops an output of the signal conditioning circuit at the second frequency to generate a fourth signal. The fourth signal is filtered.