Low Power Ripple Free Chopper Amplifier with Correlated Double Sampling De Chopping

This paper presents a new solution to obtain a spursfree high precision amplifier. The method involves input chopping and correlated double sampling signal de-chopping. The offset is removed by using DC coupling. The proposed method, verified with transistor level simulations, is applied to a rail-to-rail input amplifier with 187 dB DC gain and 13.7 A current consumption.

Many instrumentation applications need operational ampli- fiers with very high gain (more than 120 dB) and extremely low offset. These op-amps are used to obtain large voltage gain, typically 60 dB or more. Since the bandwidth of used signals is low, the speed requests are limited and often fT as low as 100 kHz is enough. The input referred offset must be in the V range and, in addition, the power consumption has to be very low to meet portable applications requirements. The above requests are conventionally satisfied by the autozero or the chopper stabilization techniques, . However, the need of ultra low power makes the autozero technique unsuitable because it is necessary to use very large autozero capacitors. The only usable method is the chopper stabilization technique that works well at low frequency, but generates spurs at multiples of the chopping frequency. The cancellation of spur tones requires on chip low pass or bandpass filters whose implementation increases the complexity and the power consumption. This paper proposes a new method that combines the chopper stabilization technique and the correlated double sampling (CDS) method to obtain spurs free operation. The correlated double sampling method is used in the autozero technique to remove the offset. On the contrary, in this paper, the CDS is used for the signal de-chopping while the offset is removed by a DC coupling

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