Buffer Op Amp to Analog-to-Digital Converter Design: Single-Ended Input, Single Supply, Transformer Coupled

Problem:
How do I buffer the input of an Analog to Digital Converter (ADC) when I have a single-ended input, single power supply and transformer coupling?

Solution:


Double click on schematic to enlarge.

A transformer T1 is again used as the coupling element. A center tap is not required. This time, however, the op amp interface is on the secondary side. Primary termination resistor RT1 is selected to match the source impedance. Secondary termination resistor RT2 is selected to match the turn ratio of the transformer and termination resistor RT1. Resistors R1 through R4 set the inverting gain of the two op amps - R1 is equal to R3, and R4 is equal to R2. Common mode point of the op amps is set by the common mode output of the ADC, decoupled by C3. R5, R6, C1, and C2 are compensation components specified on the ADC data sheet.