TRF6900
SINGLE-CHIP RF TRANSCEIVER
SLAS213C – SEPTEMBER 1999 – REVISED MAY 2000
RF mixer (continued)
↑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
–2
–0.5
–2
–1
–1
START 850 MHz
STOP 950 MHz
START 5 MHz
STOP 25 MHz
Figure 5. Typical RF Mixer Input Impedance
(S11) at Device Terminal MIX_IN
Figure 6. Typical RF Mixer Output Impedance
(S22) at Device Terminal MIX_OUT
st
1
IF amplifier
st
The 1 IF amplifier provides a typical gain of 7 dB to compensate for losses caused by a ceramic filter. The input
st
and output of the 1 IF amplifier is matched internally to 330 Ω, permitting direct connections to 330 Ω ceramic
filters. If filters with different impedances are used, an impedance matching network is required.
st
nd
A second filter can be connected between the 1 IF amplifier and the 2 IF amplifier/limiter to increase the
nd
receiver selectivity. Alternately, the RF mixer output can be directly connected to the 2 IF amplifier as shown
in Figure 7. A single ceramic filter can also be used to connect terminal 41 to terminal 39. In this case, a
dc-blocking capacitor of 0.1 µF should be used to connect terminal 44 to 42 to maximize receiver sensitivity.
BPF
External
Components
46
44
42
41
39
2nd IF
Amplifier/
Limiter
RF Mixer
1st IF
Amplifier
st
Figure 7. Bypassing the 1 IF Amplifier
st
Figure 8 and Figure 9 show the 1 IF amplifier input and output impedances, respectively.
12
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TI [ TEXAS INSTRUMENTS ]
