SWRA004A
Low-Band and High-Band Transmit
Low- and High-Band Transmit Mixer
Figure 17 details the block diagram of the transmit mixer. The TRF1500 provides a transmit mixer for down converting the system transmit signal (low-band or high-band) to a common IF for loop-back testing. The LO input for this mixer can be selected from either the low-band LO input or the high-band LO input by means of the digital control. The RF input of the transmit mixer provides a broad-band 200Ω differential input impedance over a band of 800 MHz to 2GHz and thus requires minimal external matching.
The mixer is a double-balanced Gilbert cell design with open collector outputs. The Gilbert cell structure was implemented for its robust isolation and harmonic suppression characteristics.
Figure 17. Transmit Mixer Block Diagram
Low-Band and High-Band Transmit Mixer RF Input
Figure 18 details the transmit mixer RF input configuration. The transmit mixer can be either driven single-ended or differentially. For evaluation purposes, a 4:1 transformer balun is used on the EVM to drive the transmit mixer single-ended. The input requires very little external matching. A shunt capacitor (C35) near the input port (J30) and a shunt capacitor (C36) near the transformer balun (T30) are the only input impedance matching components required.
50 | TRF1500 Integrated Dual-Band RF Receiver User’s Guide |
