26 - Application considerations and circuits for a new chopper-stabilized op amp

Abstract

The chopper-stabilized approach uses the amplifier's input to amplitude modulate an AC carrier. This carrier, amplified and synchronously demodulated back to DC, furnishes the amplifier's output. Because the DC input is translated to and amplified as an AC signal, the amplifier's DC terms have no effect on overall drift. This is the reason why chopper-stabilized amplifiers are able to achieve significantly lower time and temperature drifts than classic differential types. The most significant tradeoff is increased complexity. The chopping circuitry and sampled data operation of these amplifiers require significant attention for good results. The third generation LTC1052 monolithic chopper-stabilized amplifier is significantly better than previous monolithic chopper-stabilized amplifiers in several areas. For comparison purposes, conventional field-effect transistor input and bias current compensated bipolar types are also listed. Noise has been a particular concern with previous monolithic chopper designs. Additionally, the LTC1052's input common mode range includes V–, making single supply operation more practical. The most obvious applications are at low-level DC, where the low drift will improve performance over other amplifiers. More subtly, it is possible to exploit the LTC1052's low offset uncertainties to extend the dynamic range of circuit operation. Additional, less obvious, circuits use the LTC1052 to stabilize and enhance the performance of a variety of functions including data converters, buffers, and comparators.