A wide dynamic range mean-squared RF detector from Linear Technology is the LT5570. It provides accurate RMS (Root-Mean-Squared) power measurement of a 40MHz to 2.7GHz AC signal over 60dB dynamic range, even with a modulation crest-factor of up to 12dB. 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 fast response with a full-scale rise time of 500ns.
As nascent next-generation wireless standards such as mobile WiMAX and LTE (Long-Term Evolution) adopt more complex modulation schemes, combining OFDM (Orthogonal Frequency Division Multiplexing) and QAM (Quadrature Amplitude Modulation) to boost the data rate, it becomes increasingly difficult to accurately measure these high crest-factor signals. This problem is not just confined to wireless infrastructure, as many other wireless systems are similarly constrained by limited spectrum bandwidth. As a result, 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 the LT5570 is designed to meet these emerging challenges. The LT5570 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 0.2dB, compared to that of a CW (continuous waveform) power. The device offers 61dB dynamic range at 880MHz, and 51dB at 2.14GHz. Its linear DC output is proportional to the input power in dBm with a scaling factor of 36.5mV/dB, typical. Minimum sensitivity is -53dBm at 880MHz, and -43dBm at 2.14GHz. The device offers exceptional linearity, deviating less than ±0.5dB from the ideal log-linear straight line, and over the device’s operating temperature extremes.
The LT5570 operates from a single 5V supply, drawing a quiescent supply current of 26.5mA. A shutdown feature is provided, reducing supply current to 0.1uA. The device comes in a 10-lead 3mm x 3mm DFN surface mount package. Pricing starts at $5.75 each in 1,000 piece quantities.
