AD608
Rev. C | Page 12 of 16
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.
10.7MHz BPF Z = 330Ω
R2
330Ω
C5
0.1µF
R1
330Ω
C2
100pF
C3
100pF
C4
100pF
C1
1µF
POS
LIMO
C6
10nF
SUPPLY
2.7V TO 5.5V
POWER-UP
3V CMOS
LO INPUT
–16dBm
RF INPUT
–95dBm
TO
–15dBm
C7
18nF
16
15
12
11
10
14
13
9
1
2
5
6
7
3
4
8
AD608
VPS1
COM1
RFHI
RFLO
MXOP
LOHI
COM2
VMID
PRUP
LMOP
COM3
RSSI
IFLO
VPS2
FDBK
IFHI
R3
100Ω
R4
47kΩ
R6
51.1Ω
R5
51.1Ω
LIMITER
OUTPUT
VPOS –1V
±200mV
RSSI OUTPUT
+0.2V TO +1.8V
(20mV/dB)
+
+
+
+
+
+
+
07886-024
OFFSET-CONTROL
LOOP FILTER
BPF
TEMINATION
IF BIAS POINT
DECOUPLING
BPF REVERSE
TERMINATION
BIAS POINT
AT VPOS/2
Figure 24. Application at 10.7 MHz (the Band-Pass Filter Can Be a Toko SK107 or Murata SFE10.7)
+5V
R1
51.1Ω
R2
51.1Ω
C1
0.1µF
C2
1nF
GND
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
AD608
VPS1
COM1
RFHI
RFLO
MXOP
LOHI
COM2
VMID
PRUP
LMOP
COM3
RSSI
IFLO
VPS2
FDBK
IFHI
R3
374Ω
R4
1.5kΩ
R6
1kΩ
LOHI
RFHI
C3
1nF
R7
1130Ω
F1
C7
0.1µF
C6 0.1µF
C8 0.1µF
C9
0.2µF
R5
200Ω
C5 0.1µF
R14
8.66kΩ
R15
24.9kΩ
R13
402Ω
R12
1kΩ
CR1
CR2
R8
1kΩ
R9
1kΩ
C10
0.01µF
R11
3.3kΩ
AUDIO
PRUP
RSSI
JUMPE
F1: TOKO HCFM2–455B
F2: MURATA CFY455S
CR1, CR2: 1N60
Q1: 2N3906
F2
R10
3.3kΩ
R16
47kΩ
Q1
C11
0.1µF
C4
1nF
07886-025
Figure 25. Narrow-Band FM Application at 450 kHz or 455 kHz
