Texas Instruments TRF1500 manual High-Band RF Input, High-Band LO Input

SWRA004A

High-Band RF Input

Figure 12 details the high-band RF input configuration. The cascaded noise figure and input return loss performance of the high-band receiver section is determined primarily by the input matching network. The input matching network is designed for optimum noise figure performance, while maintaining good input return loss. A low-pass shunt-C (C20) series-L (L20) network is used for the input impedance matching. The series capacitor (C29) on the input port is used for dc blocking purposes. The end- user can optimize the input matching network for better input return loss but obtaining a better input match may degrade the overall cascaded noise figure performance.

Figure 12. High-Band RF Input Configuration

High-Band LO Input

The high-band LO signal is fed through a buffer amplifier into a differential quadrature generator, which is realized using a polyphase network. The signals generated by the polyphase network are used to drive two mixers which are injected with a common RF signal. The IF signals out of these mixers will have a 180° phase shift of the image frequency as compared to the wanted RF frequency. As a result of this 180° phase shift, the IF signals at the image frequency will cancel in the quadrature combiner. The IF signal at the desired frequency will add in the quadrature combiner.

The TRF1500 offers several methods for providing high-band LO drive. The high-band LO terminal may be directly driven either single-ended or differentially. Alternately, the high-band LO terminal may be driven by using the low-band LO output and the integrated frequency doubler.

36 TRF1500 Integrated Dual-Band RF Receiver User’s Guide