1 MHz to 8 GHz, 70 dB

Logarithmic Detector/Controller

AD8318

Rev. B

Information furnished by Analog Devices is believed to be accurate and reliable. However, no

responsibilityis assumedbyAnalogDevicesforitsuse,norforanyinfringements of patents or other

rightsofthirdpartiesthatmayresultfromitsuse.Specificationssubjecttochangewithoutnotice.No

license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.

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

©2004-2007 Analog Devices, Inc. All rights reserved.

FEATURES

Wide bandwidth: 1 MHz to 8 GHz

High accuracy: ±1.0 dB over 55 dB range (f < 5.8 GHz)

Stability over temperature: ±0.5 dB

Low noise measurement/controller output (VOUT)

Pulse response time: 10 ns/12 ns (fall/rise)

Integrated temperature sensor

Small footprint LFCSP

Power-down feature: <1.5 mW at 5 V

Single-supply operation: 5 V @ 68 mA

Fabricated using high speed SiGe process

APPLICATIONS

RF transmitter PA setpoint control and level monitoring

RSSI measurement in base stations, WLAN, WiMAX, and

radars

GENERAL DESCRIPTION

The AD8318 is a demodulating logarithmic amplifier, capable

of accurately converting an RF input signal to a corresponding

decibel-scaled output voltage. It employs the progressive

compression technique over a cascaded amplifier chain, each

stage of which is equipped with a detector cell. The device is

used in measurement or controller mode. The AD8318

maintains accurate log conformance for signals of 1 MHz to

6 GHz and provides useful operation to 8 GHz. The input range

is typically 60 dB (re: 50 Ω) with error less than ±1 dB. The

AD8318 has a 10 ns response time that enables RF burst

detection to beyond 45 MHz. The device provides unprece-

dented logarithmic intercept stability vs. ambient temperature

conditions. A 2 mV/°C slope temperature sensor output is also

provided for additional system monitoring. A single supply of

5 V is required. Current consumption is typically 68 mA. Power

consumption decreases to <1.5 mW when the device is disabled.

The AD8318 can be configured to provide a control voltage

to a VGA, such as a power amplifier or a measurement output,

from Pin VOUT. Because the output can be used for controller

applications, wideband noise is minimal.

FUNCTIONAL BLOCK DIAGRAM

TEMP

SENSOR

GAIN

BIAS

SLOPE

DET

DET

DET

DET

INHI

INLO

IV

VOUT

IV

VSET

CLPF

TEMP

VPSI

ENBL

TADJ

VPSO

CMOP

CMIP

Figure 1.

2.4

0

–65

10

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

6

–6

5

4

3

2

1

0

–1

–2

–3

–4

–5

–60 –55 –50 –45 –40 –35 –30 –25 –20 –15 –10 –5

0

5

Figure 2. Typical Logarithmic Response and Error vs. Input Amplitude at 5.8 GHz

In this mode, the setpoint control voltage is applied to VSET.

The feedback loop through an RF amplifier is closed via VOUT,

the output of which regulates the amplifier output to a magnitude

corresponding to VSET. The AD8318 provides 0 V to 4.9 V

output capability at the VOUT pin, suitable for controller

applications. As a measurement device, Pin VOUT is externally

is a decreasing linear-in-dB function of the RF input signal

amplitude.

The logarithmic slope is nominally −25 mV/dB but can be

adjusted by scaling the feedback voltage from VOUT to the

VSET interface. The intercept is 20 dBm (re: 50 Ω, CW input)

using the INHI input. These parameters are very stable against

supply and temperature variations.

The AD8318 is fabricated on a SiGe bipolar IC process and is

available in a 4 mm × 4 mm, 16-lead LFCSP for the operating