ZHCSF64B June 2016 – January 2018 ADS8910B , ADS8912B , ADS8914B
PRODUCTION DATA.
The application circuits are shown in Figure 108 and Figure 109. In both applications, the input signal is processed through a high-bandwidth, low-distortion, fully-differential amplifier (FDA) designed in a gain of 1 V/V and a low-pass RC filter before going to the ADC.
The reference voltage of 4.5 V generated by the high-precision, low-noise REF5045 circuit. The output broadband noise of the reference is heavily filtered by a low-pass filter with a 3-dB cutoff frequency of 16 Hz.
Generally, the distortion from the input driver must be at least 10 dB less than the ADC distortion. The distortion resulting from variation in the common-mode signal is eliminated by using the FDA in an inverting gain configuration that establishes a fixed common-mode level for the circuit. This configuration also eliminates the requirement of a rail-to-rail swing at the amplifier input. Therefore, these circuits use the low-power THS4551 as an input driver that provides exceptional ac performance because of its extremely low-distortion and high bandwidth specifications. In addition, the components of the charge kickback filter keep the noise from the front-end circuit low without adding distortion to the input signal.
The circuit in Figure 108 shows a fully-differential data acquisition (DAQ) block optimized for low distortion and noise using the THS4551 and ADS891xB. This front-end circuit configuration requires a differential signal at the input of the FDA and provides a differential output to drive the ADC inputs. The common-mode voltage of the input signal provided to the ADC is set by the VOCM pin of the THS4551 (not shown in Figure 108). To use the complete dynamic range of the ADC, VOCM can be set to VREF / 2 by using a simple resistive divider.
The circuit in Figure 109 shows a single-ended to differential DAQ block optimized for low distortion and noise using the THS4551 and the ADS891xB. This front-end circuit configuration requires a single-ended bipolar signal at the input of the FDA and provides a fully-differential output to drive the ADC inputs. The common-mode voltage of the input signal provided to the ADC is set by the VOCM pin of the THS4551 (not shown in Figure 109). To use the complete dynamic range of the ADC, VOCM can be set to VREF / 2 by using a simple resistive divider.