REV. B

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

which may result from its use. No license is granted by implication or

otherwise under any patent or patent rights of Analog Devices.

a

50 MHz, 80 dB Demodulating

Logarithmic Amplifier with Limiter Output

AD606

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 1999

FEATURES

Logarithmic Amplifier Performance

–75 dBm to +5 dBm Dynamic Range

≤1.5 nV/√Hz Input Noise

Usable to >50 MHz

37.5 mV/dB Voltage Output

On-Chip Low-Pass Output Filter

Limiter Performance

1 dB Output Flatness over 80 dB Range

3 Phase Stability at 10.7 MHz over 80 dB Range

Adjustable Output Amplitude

Low Power

+5 V Single Supply Operation

65 mW Typical Power Consumption

CMOS-Compatible Power-Down to 325

W typ

<5

s Enable/Disable Time

APPLICATIONS

Ultrasound and Sonar Processing

Phase-Stable Limiting Amplifier to 100 MHz

Received Signal Strength Indicator (RSSI)

Wide Range Signal and Power Measurement

PRODUCT DESCRIPTION

The AD606 is a complete, monolithic logarithmic amplifier

using a 9-stage “successive-detection” technique. It provides

both logarithmic and limited outputs. The logarithmic output is

from a three-pole post-demodulation low-pass filter and provides

a loadable output voltage of +0.1 V dc to +4 V dc. The logarith-

mic scaling is such that the output is +0.5 V for a sinusoidal

input of –75 dBm and +3.5 V at an input of +5 dBm; over this

range the logarithmic linearity is typically within

±0.4 dB. All

scaling parameters are proportional to the supply voltage.

The AD606 can operate above and below these limits, with

reduced linearity, to provide as much as 90 dB of conversion

range. A second low-pass filter automatically nulls the input

offset of the first stage down to the submicrovolt level. Adding

external capacitors to both filters allows operation at input fre-

quencies as low as a few hertz.

The AD606’s limiter output provides a hard-limited signal

output as a differential current of

±1.2 mA from open-collector

outputs. In a typical application, both of these outputs are

loaded by 200

Ω resistors to provide a voltage gain of more than

90 dB from the input. Transition times are 1.5 ns, and the

phase is stable to within

±3° at 10.7 MHz for signals from

–75 dBm to +5 dBm.

The logarithmic amplifier operates from a single +5 V supply

and typically consumes 65 mW. It is enabled by a CMOS logic

level voltage input, with a response time of <5

µs. When dis-

abled, the standby power is reduced to <1 mW within 5

µs.

The AD606J is specified for the commercial temperature range

of 0

°C to +70°C and is available in 16-lead plastic DIPs or

SOICs. Consult the factory for other packages and temperature

ranges.

FUNCTIONAL BLOCK DIAGRAM

REFERENCE

AND POWER-UP

ONE-POLE

FILTER

FINAL

LIMITER

MAIN SIGNAL PATH

11.15dB/STAGE

OFFSET-NULL

LOW-PASS FILTER

30pF

30pF

360k

360k

2pF

9.375k

9.375k

2pF

X2

TWO-POLE

SALLEN-KEY

FILTER

12 A/dB

2 A/dB

HIGH-END

DETECTORS

AD606

1.5k

1.5k

250

30k

30k

9

10

11

12

13

14

15

16

12

345

67

8

INLO

COMM

ISUM

ILOG

BFIN

VLOG

OPCM

LMLO

LMHI

LADJ

FIL2

FIL1

VPOS

PRUP

COMM

INHI

X1