The high bandwidth provided by the OPA690, while operating on a single 5-V supply, works well with high-frequency active filter designs. Again, the key additional requirement is to establish the dc operating point of the signal near the supply midpoint for highest dynamic range. See Figure 8-7 for an example design of a 5-MHz low-pass Butterworth filter using the Sallen-Key topology.

Both the input signal and the gain setting resistor are ac-coupled using 0.1-µF blocking capacitors (actually giving band-pass response with the low-frequency pole set to 32 kHz for the component values shown). As discussed for Figure 7-2, this allows the midpoint bias formed by the two 1.87-kΩ resistors to appear at both the input and output pins. The midband signal gain is set to 4 (12 dB) in this case. The capacitor to ground on the noninverting input is intentionally set larger to dominate input parasitic terms. At a gain of 4, the OPA690 on a single supply shows approximately 80-MHz small- and large-signal bandwidth. The resistor values are slightly adjusted to account for this limited bandwidth in the amplifier stage. Tests of this circuit show a precise 5-MHz, −3-dB point with a maximally flat pass band (greater than the 32-kHz ac-coupling corner), and a maximum stop-band attenuation of 36 dB at the −3-dB bandwidth of 80 MHz of the amplifier.