JAJSP64I December 2003 – October 2024 OPA695
PRODUCTION DATA
One common requirement in an IF strip is to buffer the output of a mixer with enough gain to recover the insertion loss of a narrow-band SAW filter. Figure 1-1 shows one possible configuration driving a SAW filter. Figure 7-11 shows the intercept at the 50-Ω load. Operating in the inverting mode at a voltage gain of –8 V/V, this circuit provides a 50-Ω input match using the gain set resistor, has the feedback optimized for maximum bandwidth (700 MHz in this case), and drives through a 50-Ω output resistor into the matching network at the input of the SAW filter. If the SAW filter gives a 12-dB insertion loss, a net gain of 0 dB to the 50-Ω load at the output of the SAW (which can be the input impedance of the next IF amplifier or mixer) is delivered in the pass band of the SAW filter. Using the OPA695 in this application isolates the first mixer from the impedance of the SAW filter and provides very low two-tone, 3rd-order spurious levels in the SAW filter bandwidth. Inverting operation gives the broadest bandwidth up to a gain of –12 V/V (15.6 dB). Noninverting operation gives higher bandwidth at gain settings higher than this, but also gives a slight reduction in intercept and noise figure performance.