Impact of Injected Charges, Clock Noise and Operational Amplifier Imperfections on the Sample and Hold (SH) Overall Performance

摘要

The growing use of digital processing in analog environments underlines the importance of Analog Digital Converter (ADC) occurrence in circuitry. The quality and reliability of the conversion are closely linked to the Sample and Hold (SH) performance. Actually SH is a key component in the Analog/Digital chain. The Operational Amplifier being at the heart of the SH influences its output and subsequently impacts the reliability and quality of the conversion. In this paper we present the impact of both Operational Amplifier intrinsic characteristics and external factors such as injected charges, and clock noise on the SH overall performance. We limit our consideration to the offset and parasite capacities as the only relevant Operational Amplifier intrinsic characteristics. We’ll introduce the Operational Amplifier and SH functional characteristics then address the impact of each of these parameters on the SH output which the ADC works on. A behavioral description of the Operational Amplifier based on the Verilog-A language under Cadence approach is used. Furthermore a behavioral/analog mixed description is considered for the SH: the Operational Amplifier described behaviorally in Verilog-A is associated to analog components in Cadence libraries and CMOS switches act as SH. However this simplistic approach doesn’t reflect all the challenges involved, because it is not enough to connect a SH to ADC to flawlessly digitalize an analog signal. The SH architecture and the Operational Amplifier characteristics play also a role for a reliable sampling and therefore a good quality conversion prospect.In this study the SH performance is evaluated through its non-linearity which in turn determines the sampling accuracy a key factor for a conversion. This study is as shown that small amplitude signals are more sensible to sampling errors related to Operational Amplifier offset. Furthermore the stray capacities attenuate the SH signal output. The injected charges and the clocknoise as strongly interrelated contribute to the non-linearity of the conversion chain.