ZHCSD79A January 2015 – August 2019 ADS54J54
PRODUCTION DATA.
The analog inputs of the ADS54J54 must be fully differential and biased to a desired common mode voltage, VCM. Therefore, there will be a signal conditioning circuit for each of the analog inputs. If the amplitude of the input circuit is such that no gain is needed to make full use of the full-scale range of the ADC, then a transformer coupled circuit as in Figure 101 may be used with good results. The transformer coupling is inherently low-noise, and inherently AC-coupled so that the signal may be biased to VCM after the transformer coupling. If signal gain is required, or the input bandwidth is to include the spectrum all the way down to DC such that AC coupling is not possible, then an amplifier-based signal conditioning circuit would be required.
By using the simple drive circuit of Figure 101, uniform performance can be obtained over a wide frequency range. The buffers present at the analog inputs of the device help isolate the external drive source from the switching currents of the sampling circuit.