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Matched Dual-channel 6 GHz RMS Power Detector

February 5, 2011
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The Linear Technology LTC5583 is a 40 MHz to 6 GHz dual-channel, matched RMS power detector, offering over 55 dB isolation at 2.14 GHz. In RF power amplifier (PA) applications, the LTC5583 provides a simple solution for accurately measuring forward power, reverse power and voltage standing wave ratio (VSWR). The device comprises a pair of 60 dB dynamic range RMS detectors that are matched to 1.25 dB. This provides accurate RF power measurement of high crest-factor signals such as those used in LTE, WiMAX, W-CDMA, TD-SCDMA and CDMA2000 3G or 4G base stations and other high-performance radios employing complex modulation waveforms. Each channel can detect signals accurately from as small as -58 to 2 dBm in a log-linear response with a typical linearity of better than 0.5 dB covering all cellular frequency bands. At higher frequencies, the device is capable of providing 47 dB of useful dynamic range up to 6 GHz. Unique to the LTC5583, each detector simultaneously tracks the envelope of the modulated input waveform, providing on-chip capability to measure both peak and average signal power.


The LTC5583 has best-in-class channel-to-channel isolation of over 55 dB at 2.14 GHz when driven differentially. Unlike other detectors, the LTC5583 can operate single-ended for RF input frequencies up to 2.14 GHz, requiring no external balun transformers. This configuration greatly reduces costs without trading off dynamic range and provides isolation better than 40 dB. An integrated amplifier measures the difference between the two detector outputs. For applications where one RF input is measuring the forward power and the other the reflected power, the difference output provides real time VSWR results. The two matched detectors are also useful in applications such as monitoring and controlling RF amplifier stage gain. The LTC5583's matching and isolation performance minimize calibration requirements, thus simplifying designs and reducing costs.

Figure 1 Output voltage and linear error vs. RF input power at 2140 MHz (CW inputs, single-ended drive.

The detectors exhibit outstanding temperature performance. Each detector maintains accuracy of 1 dB error over a 53 dB dynamic range over its specified operating temperature range of -40° to 85°C (see Figure 1). This enables the LTC5583 to be used in rugged environments such as Remote Radio Units (RRU) or Outdoor Units (ODU) deployed on cellular towers. Moreover, the device has on-chip provisions for first- and second-order temperature compensation, which enable easy calibration for improved temperature performance. Typical applications include VSWR monitor, MIMO transmit power control, base station PA control, transmit and gain control, and RF instrumentation.

The LTC5583 operates on a single 3.3 V supply with total current consumption of 80.5 mA. This 266 mW is 25 percent lower power than other available solutions. The device has an enable pin, allowing the chip to power down. In shutdown mode, the device draws a maximum current of 10 uA. The LTC5583 is available in a 4 4 mm 24-pin QFN package.

Linear Technology,
Milpitas, CA
(408) 432-1900
www.linear.com

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