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RF power detector

OFDM (orthogonal frequency division multiplexing) and QAM (quadrature amplitude modulation) yield high crest-factor signals (high PAR, or peak-to-average ratio), which are difficult to measure accurately. Linear Technology has introduced the LT5570, a widedynamic- range mean-squared RF detector that provides accurate RMS power measurement of a 40-MHz to 2.7-GHz signal over 60 dB dynamic range, even with a modulation crest factor of up to 12 dB. Measurement accuracy is ±0.5 dB over its full dynamic range and over a temperature range of -40°C to +85°C. Today’s basestation designs need to acquire power-level data within 1 µsec, for which Linear offers a full-scale rise time of 500 nsec. Cable networks, microwave datalinks, satellite communications, and military radios have similar needs to LTE cellular and WiMAX transmitters, Linear says: cable networks already use 256 QAM, moving to 1024 QAM. Even if the input waveform has high crestfactor content, such as a four-carrier W-CDMA modulated waveform, its RMS conformance accuracy is typically within 0.2 dB, compared to that of a CW (continuous waveform) power. The device has 61 dB dynamic range at 880 MHz and 51 dB at 2.14 GHz. Its linear DC output is proportional to the input power in dBm with a scaling factor of 36.5 mV/dB, typical. Minimum sensitivity is -53 dBm at 880 MHz and -43 dBm at 2.14 GHz. It operates from a single 5V supply and uses 26.5 mA, with shutdown to 0.1 µA. In a 10-lead 3 x 3 mm DFN package it costs $5.75 (1000).

Linear Technology, www.linear.com