Texas Instruments TRF1500 - Manual (Page 50)

SWRA004A
TRF1500 Integrated Dual-Band RF Receiver User’s Guide 51
Figure 18. Low- and High-Band Transmit Mixer RF Input Configuration
Low- and High-Band Transmit Mixer IF Output
Figure 19 details the transmit mixer IF output configuration. The
transmit mixer has a differential IF output with a 1k
Ω
differential
impedance. For evaluation purposes, a 16:1 transformer balun,
with an insertion loss of 1.8 dB, is used to transform the 1k
Ω
differential output to a single-ended output which is then matched
to 50
Ω
.
The supply voltage (VCC) is applied to the IF pins with pull up
inductors (L30, L31). A low-pass filter network is provided prior to
the balun. This filter also acts as part of the impedance matching
network. The IF response is shaped by the shunt inductor (L50)
after the transformer balun. L50 is also used to block unwanted
noise that could be reflected back to the mixer. The series
capacitor (C50), near the TX_IF_OUT port, is used as a dc block
for evaluation purposes and does not have to be implemented in
the end-users system.
Figure 19. Low- and High-Band Transmit Mixer IF Output Configuration