To enable base stations to transmit stable and accurate power levels for optimal performance and coverage, Linear Technology has developed a true root-mean-squared (RMS)) RF power detector with wide dynamic range using its second generation RF bipolar process. The LT5570 provides not only accurate power measurements of high crest-factor signals, but it maintains accuracy over temperature. According to the supplier, it is designed to provide 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. Thus, it offers measurement accuracy of ±0.5dB over its full dynamic range and over a temperature range of –40 °C to +85 °C. Moreover, the device allows exceptionally fast response with a full-scale rise time of 500 ns, stated product marketing manager James Wong

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As nascent next-generation wireless standards such as mobile WiMAX and long-term evolution (LTE) adopt more complex modulation schemes, combining orthogonal frequency division multiplexing (OFDM) and quadrature amplitude modulation (QAM) to boost the data rate, it becomes increasingly difficult to accurately measure these high crest-factor signals, noted Wong. This problem is not just confined to wireless infrastructure, as many other wireless systems are similarly constrained by limited spectrum bandwidth, added Wong. As a result, he said, there is an ongoing need for higher order modulation to increase data rates. Cable networks, microwave datalinks, satellite communications, and military radios have similar needs, and LT5570 is designed to meet these emerging challenges.

The new RF detector provides a DC output proportional to the RMS value of the input signal power. Even if the input waveform has high crest-factor content, such as a 4-carrier W-CDMA modulated waveform, its RMS conformance accuracy is typically within 0.2 dB, compared to that of a continuous waveform (CW) power. The device offers 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. The device offers exceptional linearity, deviating less than + 0.5 dB from the ideal log-linear straight line, and over the device’s operating temperature extremes.

It operates from a single 5 V supply, drawing a quiescent supply current of 26.5 mA. A shutdown feature reduces supply current to 0.1 µA. The device comes in a 10-lead 3 mm x 3 mm DFN surface mount package. And pricing starts at $5.75 each in 1,000 piece quantities.

Meanwhile, the manufacturer is also readying a next generation version based on silicon germanium bipolar process with capability to handle frequencies up to 4 GHz. The next generation RF detector is expected to be unveiled in less than a year from now.