Considerations for the design of switched-capacitor circuits using precise-gain operational amplifiers

Abstract

Standard design of switched-capacitor (SC) networks assumes operation with infinite gain and infinite bandwidth op amps. However, in the op amp design a tradeoff exists between the speed and the gain. As a consequence when a high sampling frequency is used, the needed large bandwidth limits the op amp gain to low values, therefore limiting the achievable accuracy. For this reason standard design is less feasible for high-sampling frequency. For these cases alternative design approaches are needed that address the op amp design tradeoff between speed-and-gain, allowing the frequency range of SC networks to be extended, A possible alternative is the precise op amp gain (POG) design approach which has been already demonstrated with the realization of a 150 MHz SC filter. The POG design approach consists of designing high-frequency SC networks taking into account the precise gain value of the op amps as a parameter in the capacitor design. The standard op amp design tradeoff between speed-and-gain is changed into the POG design tradeoff between speed-and gain precision which is more affordable in high-frequency op amps. In this brief, the POG design approach is developed in detail and practical considerations regarding its possibility and limits are reported.