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

摘要

Standard design of switched-capacitor (SC) networks assumesnoperation with infinite gain and infinite bandwidth op amps. However, innthe op amp design a tradeoff exists between the speed and the gain. As anconsequence when a high sampling frequency is used, the needed largenbandwidth limits the op amp gain to low values, therefore limiting thenachievable accuracy. For this reason standard design is less feasiblenfor high-sampling frequency. For these cases alternative designnapproaches are needed that address the op amp design tradeoff betweennspeed-and-gain, allowing the frequency range of SC networks to benextended, A possible alternative is the precise op amp gain (POG) designnapproach which has been already demonstrated with the realization of an150 MHz SC filter. The POG design approach consists of designingnhigh-frequency SC networks taking into account the precise gain value ofnthe op amps as a parameter in the capacitor design. The standard op ampndesign tradeoff between speed-and-gain is changed into the POG designntradeoff between speed-and gain precision which is more affordable innhigh-frequency op amps. In this brief, the POG design approach isndeveloped in detail and practical considerations regarding itsnpossibility and limits are reported