Low Power Mixer/Limiter/RSSI
3 V Receiver IF Subsystem
AD608
The RF and local oscillator (LO) bandwidths both exceed
500 MHz. In a typical IF application, the AD608 can accept the
output of a 240 MHz surface acoustic wave (SAW) filter and down-
convert it to a nominal 10.7 MHz IF with a conversion gain of
24 dB (ZIF = 165 Ω). The AD608 logarithmic/limiting amplifier
section handles any IF from low frequency (LF) up to 30 MHz.
FEATURES
Mixer
−15 dBm, 1 dB compression point
−5 dBm IP3
24 dB conversion gain
>500 MHz input bandwidth
Logarithmic/limiting amplifier
80 dB RSSI range
3ꢀ phase stability over 80 dB range
Low power
The mixer is a doubly balanced gilbert-cell mixer and operates
linearly for RF inputs spanning −95 dBm to −15 dBm. It has a
nominal −5 dBm third-order intercept. An on-board LO pre-
amplifier requires only −16 dBm of LO drive. The current output
of the mixer drives a reverse-terminated, industry-standard
10.7 MHz, 330 Ω filter.
21 mW at 3 V power consumption
CMOS-compatible power-down to 300 μW typical
200 ns enable/disable time
The nominal logarithmic scaling is such that the output is +0.2 V
for a sinusoidal input to the IF amplifier of −75 dBm and +1.8 V
at an input of +5 dBm; over this range, the logarithmic confor-
mance is typically 1 dB. The logarithmic slope is proportional
to the supply voltage. A feedback loop automatically nulls the
input offset of the first stage down to the submicrovolt level.
APPLICATIONS
PHS, GSM, TDMA, FM, or PM receivers
Battery-powered instrumentation
Base station RSSI measurements
The AD608 limiter output provides a hard-limited signal output
at 400 mV p-p. The voltage gain of the limiting amplifier to this
output is more than 100 dB. Transition times are 11 ns and the
phase is stable to within 3ꢀ at 10.7 MHz for signals from −75 dBm
to +5 dBm.
GENERAL DESCRIPTION
The AD608 provides a low power, low distortion, low noise mixer
as well as a complete, monolithic logarithmic/limiting amplifier
that uses a successive-detection technique. In addition, the AD608
provides both a high speed received signal strength indicator
(RSSI) output with 80 dB dynamic range and a hard-limited
output. The RSSI output is from a two-pole postdemodulation
low-pass filter and provides a loadable output voltage of 0.2 V to
1.8 V. The AD608 operates from a single 2.7 V to 5.5 V supply
at a typical power level of 21 mW at 3 V.
The AD608 is enabled by a CMOS logic-level voltage input,
with a response time of 200 ns. When disabled, the standby
power is reduced to 300 μW within 400 ns.
The AD608 is specified for the industrial temperature range of
−25ꢀC to +85ꢀC for 2.7 V to 5.5 V supplies and −40ꢀC to +85ꢀC for
3.0 V to 5.5 V supplies. This device comes in a 16-lead plastic SOIC.
FUNCTIONAL BLOCK DIAGRAM
3dB NOMINAL
INSERTION LOSS
110dB LIMITER GAIN
90dB RSSI
24dB MIXER GAIN
RSSI OUTPUT
20mV/dB
RSSI
7 FULL-WAVE
IF INPUT
11
12
±6mA MAX OUTPUT
(±890mV INTO 165Ω)
RECTIFIER CELLS
–75dBm TO
0.2V TO 1.8V
2
+15dBm
2MHz
LPF
5
6
RFHI
COM3
VPS2
MIXER
10.7MHz
BAND-PASS
FILTER
IFHI
RF INPUT
MXOP
–95dBm TO
7
8
9
14 +2.7V TO 5.5V
1
–15dBm
BPF
DRIVER
LMOP
5-STAGE IF AMPLIFIER
(16dB PER STAGE)
330Ω
15 LIMITER
OUTPUT
400mV p-p
330Ω
RFLO
10nF
LO
PREAMP
VMID
FINAL
LIMITER
10
13
+
IFLO
100nF
100Ω
MIDSUPPLY
IF BIAS
FDBK
18nF
±50µA
BIAS
AD608
VPS1 COM1
LOHI COM2
4
PRUP
1
2
3
16
2.7V TO
5.5V
LO INPUT
–16dBm
CMOS LOGIC
INPUT
1
–15dBm = ±56mV MAXIMUM FOR LINEAR OPERATION.
39.76µV RMS TO 397.6mV RMS FOR ±1dB RSSI ACCURACY.
2
Figure 1.
Rev. C
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©1996–2009 Analog Devices, Inc. All rights reserved.
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