AD8315

Complete RF Detector/Controller Function
>50 dB Range at 0.9 GHz (49 dBm to +2 dBm re 50
)
Accurate Scaling from 0.1 GHz to 2.5 GHz
Temperature-Stable Linear-in-dB Response
Log Slope of 23 mV/dB, Intercept at 60 dBm at 0.9 GHz
True Integration Function in Control Loop
Low Power: 20 mW at 2.7 V, 38 mW at 5 V
Power Down to 10.8 mW

The AD8315 is a complete low cost subsystem for the precise control of RF power amplifiers operating in the frequency range 0.1 GHz2.5 GHz and over a typical dynamic range of 50 dB. It is intended for use in cellular handsets and other battery-operated wireless devices. The log amp technique provides a much wider measurement range and better accuracy than controllers using diode detectors. In particular, its temperature stability is excellent over a specified range of 30C to +85C.

AD8315's high sensitivity allows control at low signal levels, thus reducing the amount of power that needs to be coupled to the detector.

For convenience, the signal is internally ac-coupled. This high-pass coupling, with a corner at approximately 0.016 GHz, determines the lowest operating frequency. Thus, the source may be dc grounded.

The AD8315 provides a voltage output, VAPC, that has the voltage range and current drive to directly connect to most handset power amplifiers' gain control pin. VAPC can swing from 250 mV above ground to within 200 mV below the supply voltage. Load currents of up to 6 mA can be supported.

The setpoint control input is applied to pin VSET and has an operating range of 0.25 V1.4 V. The associated circuit determines the slope and intercept of the linear-in-dB measurement system; these are nominally 23 mV/dB and 60 dBm for a 50 W termination (73 dBV) at 0.9 GHz. Further simplifying the application of the AD8315, the input resistance of the setpoint interface is over 100 MW, and the bias current is typically 0.5 mA.

The AD8315 is available in MSOP and lead frame chip scale (LFCSP) packages and consumes 8.5 mA from a 2.7 V to 5.5 V supply. When powered down, the sleep current is 4 mA.