100 MHz−2.7 GHz, 45 dB

RF Log Detector

Preliminary Technical Data

AD8312

PrA

10/29/2004

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FEATURES

Complete RF Detector Function

Typical Range : −45 dBm to 0 dBm re 50 Ω

Frequency Response from 100 MHz to 2.7 GHz

Temperature-Stable Linear-in-dB Response

Accurate to 2.7 GHz

Rapid Response: 70 ns to a 10 dB Step

Low Power: 12 mW at 2.7 V

APPLICATIONS

Cellular Handsets (GSM, CDMA, WCDMA)

RSSI and TSSI for Wireless Terminal Devices

Transmitter Power Measurement

PRODUCT DESCRIPTION

The AD8312 is a complete low cost subsystem for the

measurement of RF signals in the frequency range of 100 MHz

to 2.7 GHz, with a typical dynamic range of 45 dB, intended for

use in a wide variety of cellular handsets and other wireless

devices. It provides a wider dynamic range and better accuracy

than possible using discrete diode detectors. In particular, its

temperature stability is excellent over the full operating range of

−40°C to +85°C.

Its high sensitivity allows measurement at low power levels, thus

reducing the amount of power that needs to be coupled to the

detector. It is essentially a voltage-responding device, with a

typical signal range of 1.25 mV to 224 mV rms or −45 dBm to 0

dBm re 50 Ω.

For convenience, the signal is internally ac-coupled, using a 5

pF capacitor to a load of 3 kΩ in shunt with 2 pF. This high-

pass coupling, with a corner at approximately 16 MHz,

determines the lowest operating frequency. Thus, the source

may be dc-grounded.

The AD8312 output, called VOUT, increases from close to

ground to about 1.2 V as the input signal level increases from

1.25 mV to 224 mV. This output is intended for use in

measurement mode. Consult the Applications section of this

data sheet for information on use in this mode. A capacitor may

be connected between the VOUT and CFLT pins when it is

desirable to increase the time interval over which averaging of

the input waveform occurs.

The AD8312 is available in a 6-lead wafer-level chip scale

package, 1.0 mm x 1.5 mm, and consumes 4.5 mA from a 2.7 V

to 5.5 V supply.

FUNCTIONAL BLOCK DIAGRAM

Figure 1.