TRF6900
SINGLE-CHIP RF TRANSCEIVER
SLAS213C – SEPTEMBER 1999 – REVISED MAY 2000
detailed description
low-noise amplifier
The low-noise amplifier (LNA) provides a typical gain of 13 dB and a typical noise figure of 3.3 dB.
Two operating modes, normal and low-gain mode, can be selected. The normal operation mode is selected
when maximum sensitivity at low input levels is required. If high RF input levels are applied to the TRF6900,
the LNA should be operated in the low-gain mode. This ensures a minimum of nonlinear distortions in the overall
receiver chain.
↑1
U
↑1 U
CH1 S11
CH1 S22
1
1
0.5
2
0.5
2
5
5
CAL
OFS
CAL
OFS
0
0.2
0.5
1
2
5
10
0
0.2
0.5
1
2
5
10
1
CPL
CPL
–5
–5
1
FIL
1k
FIL
1k
–0.5
–0.5
–2
–2
–1
–1
START 850 MHz
STOP 950 MHz
START 850 MHz
STOP 950 MHz
Figure 3. Typical LNA Input Impedance (S11)
at Device Terminal LNA_IN
Figure 4. Typical LNA Output Impedance
(S22) at Device Terminal LNA_OUT
The low impedance of the LNA input can be easily matched to 50 Ω to interface with a filter or an RF switch.
At the LNA open collector output, a filter network can be used for image suppression as well as impedance
matching.
RF mixer
The RF mixer is designed to operate with the on-chip VCO. If an external LO is used, a typical drive level of
–10 dBm should be applied at the VCO input terminal. The mixer is a conventional double-balanced Gilbert cell
mixer designed to provide a high IP3, typically 1 dBm.
Since the mixer output’s push-pull amplifier has a 330 Ω output impedance, a conventional 330 Ω ceramic filter
can be directly connected to the output without additional matching. The mixer output can also be directly
nd
connected to the 2 IF amplifier/limiter input terminal, IF2_IN, through a single conventional 330 Ω ceramic
st
filter, thus bypassing the 1 IF amplifier.
Figure 5 and Figure 6 show the RF mixer input and output impedances, respectively.
11
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