U3741BM Datasheet, PDF (5/25 Pages) ATMEL Corporation – UHF ASK RECEIVER IC

U3741BM
8 _LNAGND
U3741BM
C3
L
9 _{LNA_N}
22p
25n
8 _LNAGND
U3741BM
C3
L
9 _{LNA_N}
47p
25n
f_RF = 433.92 MHz
C16
C17
100p
8.2p
L3
27n
TOKO LL2012
F27NJ
f_RF = 315 MHz
C16
C17
100p
22p
L3
47n
TOKO LL2012
F47NJ
RF_IN
L2
TOKO LL2012
F33NJ
1 _IN
B3555
OUT
C2
33n
2 _{IN_GND}
OUT_GND
CASE_GND
8.2p
3,4 7,8
5
6
14105
RF_IN
L2
TOKO LL2012
F82NJ
1 _IN
B3551
OUT ⁵
C2
82n
2 _{IN_GND}
OUT_GND ⁶
CASE_GND
10p
3,4 7,8
14106
Figure 5. Input matching network with SAW filter
f_RF = 433.92 MHz
15p
25n
8 _LNAGND
U3741BM
9 _{LNA_N}
f_RF = 315 MHz
33p
25n
8 _LNAGND
U3741BM
9 _{LNA_N}
RF_IN
RF_IN
3.3p
100p
22n TOKO LL2012
F22NJ
14107
3.3p
100p
39n TOKO LL2012
F39NJ
14108
Figure 6. Input matching network without SAW filter
Please notify that for all coupling conditions (see
figures 5 and 6), the bond wire inductivity of the LNA
ground is compensated. C3 forms a series resonance
circuit together with the bond wire. L = 25 nH is a feed
inductor to establish a DC path. Its value is not critical but
must be large enough not to detune the series resonance
circuit. For cost reduction this inductor can be easily
printed on the PCB. This configuration improves the
sensitivity of the receiver by about 1 dB to 2 dB.
Analog Signal Processing
IF Amplifier
The signals coming from the RF front end are filtered by
the fully integrated 4th-order IF filter. The IF center
frequency is f_IF = 1 MHz for applications where
f_RF = 315 MHz or f_RF = 433.92 MHz is used. For other
RF input frequencies refer to table 1 to determine the
center frequency.
The U3741BM is available with 2 different IF
bandwidths. U3741BM-M2, the version with
B_IF = 300 kHz, is well suited for ASK systems where the
TEMIC PLL transmitter U2741B is used. The receiver
U3741BM - M3 employs an IF bandwidth of
f_IF = 600 kHz. This version can be used together with the
U2741B in FSK and ASK mode. If used in ASK
applications, it allows higher tolerances for the receiver
and PLL transmitter crystals. SAW transmitters exhibit
much higher transmit frequency tolerances compared to
PLL transmitters. Generally, it is necessary to use
B_IF = 600 kHz together with such transmitters.
Rev. A1, 15-Oct-98
5 (25)
Preliminary Information