1 MHz to 8 GHz, 60 dB Logarithmic

Detector/Controller

AD8318

Rev. A

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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 CSP package

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 radar

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.

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.

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 magni-

output capability at the VOUT pin, suitable for controller

applications. As a measurement device, Pin VOUT is externally

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 package, for the