As Figure 2-1 shows, before the verification analysis can start, the design must first complete the attenuation and input buffer stage. The important design goals to remember here are a single-ended ±10-V input signal is translated into a ± 2.5-V differential signal for the ADC input and the input impedance must be > 100 kΩ.

For the input buffer, the LMP7704-SP device was selected. The resistor divider network of the attenuation stage brings the signal level down by a factor of four. The input signal generator VG1 is set to 240-kHz sine wave with ±10-V amplitude.

Figure 2-1 Addition of Attenuation Stage and Input Buffer Stage to the FDA Circuit

Figure 2-2 shows the selection of Transient… in the Analysis menu of TINA-TI and setting the simulation window from "0" to "100u" (100 μs).

Figure 2-2 Running the Transient Analysis From 0 to 100 μs

The returned waveform in Figure 2-3 shows that the single-ended input signal with an amplitude of 10 V results into a differential output signal with an amplitude of 2.5 V. This amplitude takes advantage of the full input voltage range of the ADC for the best possible resolution.

Figure 2-3 Simulation of FDA Output Voltage VOUTdiff Versus Input Signal VG1