AD608
APPLICATIONS INFORMATION
Figure 24 shows the AD608 configured for operation in a digital
system at a 10.7 MHz IF. The input and output impedance of the
filter are parallel terminated using 330 Ω resistors, and the
conversion gain is 24 dB. The RF port is terminated in 50 Ω; in
a typical application, the input is matched to a SAW filter using
the impedance data provided in Table 5.
Figure 25 shows the AD608 configured for narrow-band FM
operation at a 450 kHz or 455 kHz with an external discriminator.
The IF filter has 1500 Ω input and output impedances—the
input is matched via a resistive divider, and the output is
terminated in 1500 Ω. The discriminator requires a 1 V p-p
drive from a 1 kΩ source impedance, which in Figure 25 is
provided by a Class A amplifier with a gain of 2.5.
VPOS
SUPPLY
2.7V TO 5.5V
C1
1µF
1
2
3
4
5
6
7
VPS1
PRUP 16
R4
POWER-UP
3V CMOS
47kΩ
LO INPUT
–16dBm
C2
COM1
LOHI
LMOP 15
VPS2 14
FDBK 13
COM3 12
RSSI 11
IFLO 10
100pF
LIMO
LIMITER
OUTPUT
VPOS –1V
±200mV
R5
51.1Ω
COM2
RFHI
+
C7
R3
18nF
100Ω
C3
100pF
RF INPUT
RFLO
MXOP
–95dBm
TO
RSSI OUTPUT
+0.2V TO +1.8V
(20mV/dB)
C4
100pF
R6
–15dBm
51.1Ω
8
VMID
IFHI
9
+
C6
10nF
AD608
10.7MHz BPF Z = 330Ω
BIAS POINT
AT VPOS/2
OFFSET-CONTROL
LOOP FILTER
R2
330Ω
R1
330Ω
+
C5
0.1µF
BPF REVERSE
TERMINATION
BPF
TEMINATION
IF BIAS POINT
DECOUPLING
Figure 24. Application at 10.7 MHz (the Band-Pass Filter Can Be a Toko SK107 or Murata SFE10.7)
JUMPER
PRUP
R16
+5V
GND
R13
47kΩ
R14
402Ω
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VPS1
PRUP
LMOP
8.66kΩ
C1
C5 0.1µF
R10
3.3kΩ
F2
0.1µF
COM1
Q1
LOHI
AUDIO
C8 0.1µF
R1
C2
LOHI
COM2
RFHI
VPS2
FDBK
COM3
RSSI
IFLO
IFHI
R8
R12
1kΩ
C11
0.1µF
R15
24.9kΩ
51.1Ω
1nF
CR1
CR2
1kΩ
R11
3.3kΩ
C10
0.01µF
C9
0.2µF
R9
1kΩ
R6
1kΩ
RFHI
R5
200Ω
R2
51.1Ω
C3
1nF
RFLO
MXOP
VMID
RSSI
C6 0.1µF
C4
1nF
R3
374Ω
AD608
F1: TOKO HCFM2–455B
F2: MURATA CFY455S
CR1, CR2: 1N60
R7
1130Ω
R4
1.5kΩ
F1
Q1: 2N3906
C7
0.1µF
Figure 25. Narrow-Band FM Application at 450 kHz or 455 kHz
Rev. C | Page 12 of 16
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