1 MHz – 8 GHz, 60 dB

Logarithmic Detector/Controller

AD8318

Rev. 0

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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 10/12 ns (fall/rise)

Integrated temperature sensor

Small footprint CSP package

Power-down feature: <1.5 mW at 5 V

Single-supply operation: 5V @ 68 mA

Fabricated using high speed SiGe process

APPLICATIONS

RF transmitter PA setpoint control and level monitoring

RSSI measurement in base stations, WLAN, radar

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 can be

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 60 MHz. The device provides

unprecedented logarithmic intercept stability versus ambient

temperature conditions. A 2 mV/K 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. Since the output can be used for controller

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.

applications, special attention has been paid to minimize

wideband noise. 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 AD8318 provides 0 V to 4.9 V output capability at the

VOUT pin, suitable for controller applications. As a

measurement device, VOUT is externally connected to

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-pin LFCSP package, for