对运算放大器作为模数转换器的输入放大器进行评估.pdfVIP

Texas Instruments Incorporated Data Acquisition Evaluating operational amplifiers as input amplifiers for A-to-D converters By James Karki Application Specialist, Operational Amplifiers This application note describes a method for comparing number of bits) is a key ac parameter used for ADCs. It is the ac performance of the TI TLV2462 and TLV2772 oper- calculated based on SINAD (signal to noise + distortion) ational amplifiers to the TI TLV2544/TLV2548 analog-to- in dB, where digital converter. Amplifiers like the TLV2462 and TLV2772 SINAD − 1.76 are used to condition the signal input to ADCs (TLV2544/ ENOB = . TLV2548). Normally the functions performed include 6.02 level shifting, impedance matching and amplification. The By measuring the THD+N (total distortion + noise) in dB drive amplifier is the link between the input source and of the TLV2462 and TLV2772 in different circuit topolo- the ADC. gies and substituting THD+N for SINAD when calculating When selecting an amplifier, ac performance factors ENOB, the amplifier’s performance is directly comparable such as bandwidth, slew rate, noise and distortion drive to the TLV2544/TLV2548 ADC. the decision-making process with dc errors considered secondarily. One of the difficulties that arises during Test circuits amplifier selection is that op amps are not normally The input to the TLV2544/TLV2548 ADC is modeled as specified in the same manner as ADCs. ENOB (effective shown in Figure 1. During sampling the input is active