To implement a differential transimpedance output interface to the PCM1792A DAC, the following requirements must be met:
- The center current of the DAC must be considered to hold the DAC output voltage at ground. Using an FDA controls the output side common-mode voltage, but the input common-mode voltage must also be controlled to ground.
- A direct means of sinking the center current is to add a pulldown resistor at the DAC outputs to a negative supply. Generating a ±2.5-V supply for this current sink requirement and the THS4551 is accomplished with the LM27762.
- The transimpedance gain can be set using the feedback resistors of the THS4551 FDA. These resistors are very flexible, but when set, the bandwidth in this stage is set to 88 kHz using a feedback capacitor in parallel with the resistive gain element.
- When the feedback capacitor is set, a differential input capacitor is added to increase the high-frequency noise gain for the overall loop gain stability.
- These frequency response control capacitors interact with the inductive open-loop output impedance to form a high-frequency resonance. Adding a small series resistor to the feedback capacitor paths reduces this effect.