HIGH-SPEED, HIGH-FREQUENCY power measurements call for agile power detectors, typically based on fast diodes. The LTC5564 RF power detector from Linear Technology is such a detector, built around a fast Schottky diode peak detector, capable of making power measurements across a frequency range of 600 MHz to 15 GHz with a response time of only 7 ns. The temperature-compensated, quick-responding Schottky diode detector can measure precise power levels across an amplitude range of -24 to +16 dBm on pulsed, modulated, and transient signals.

The LTC5564 RF power detector is housed in a compact 3 x 3 mm 16-lead QFN package (see figure). But it is more than just a diode detector, since the package also holds a fast operational amplifier with selectable gain and a high-speed comparator with latch enable and typical response time of 9 ns. In operation, an RF input signal is peak detected and then sensed by both the comparator and the operational amplifier. The diode detector and programmable- gain opamp combine to provide a demodulation bandwidth of 75 MHz for wide envelope detection when detecting the power levels of signals with complex modulation formats. The LTC5564's programmable-gain output amplifier provides four gain settings, digitally controlled by two binary-weighted logic input pins. The fast opamp boasts a 350-V/s slew rate.

The RF power detector incorporates temperature compensation circuitry for stable performance from -40 to +85C. It should be noted that the programmable gain settings, while supporting operation over the wide input signal range, do impact the response time. The 7-ns response time is achieved with the initial gain setting. As the gain settings are increased to Gain 2, Gain 3, and Gain 4 settings, the response times "slow" to 9, 11, and 14 ns, respectively. The different gain settings are used to match the detector input sensitivity to all signal levels down to -24 dBm.

The LTC5564 RF power detector also crams a high-speed comparator with latch enable and typical response time of 9 ns into that tiny package. The fast on-chip comparator allows a user to set the threshold voltage, to create different trip points. The comparator's output can be latched by asserting a latch-enable pin, enabling fast capture of a transient or short-duration signal event or fault condition. Inclusion of the comparator allows fast timing measurements with rapid response in fault detection and RF power measurements.

The LTC5564 RF power detector can serve any number of largely commercial applications, from signal-presence detectors in 2.4- GHz wireless local-area networks (WLANs), in radar detectors, and for power and signal detection in 5.8- GHz Industrial-Scientific-Medical (ISM) band radios. The LTC5564 RF power detector can operate from a single +3.3 or +5.0 VDC supply. The detector exhibits current draw of typically 44 mA under normal operating conditions. P&A: $2.90 each (1000 qty.); stock. Linear Technology Corp., 1630 McCarthy Blvd., Milpitas, CA 95035-7417; (408) 432-1900, FAX: (408) 434-0507, www.linear.com. JB