Linear releases 100MHz to 40GHz log RMS power detector

Linear Technology is aiming at RF and microwaves with a log-responding RMS to DC converter chip which can achieve 1dB accuracy and 35dB dynamic range.

Dubbed LTC5596, it responds at 29mV/dB from -37 to –2dBm, at better than ±1dB error over -40 to 125°C from 200MHz to 30GHz, with ±1dB flatness.

Linear dynamic range is 35dB with error under ±1dB.

When used across 100MHz to 40GHz, there is a reduction in accuracy at the frequency extremes, however the input remains internally matched to 50Ω.

Crest factors as high as 12dB can be accommodated, as can waveforms that exhibit a significant variation in crest factor over the measurement.

“Modern 4G and 5G broadband communications systems employ high-order multi-tone OFDM modulation” said the firm. “Traditionally, microwave Schottky diodes are used as the detector element. They face serious shortcomings when rectifying the RF or microwave signals while measuring only the peak of the waveform, which grossly misrepresents the real power of the signal.”

With RMS detector, root-mean-square of the waveform is calculated by an analogue circuit, then the result if averaged to derive a power representation of the input signal, regardless of modulation type, number of carriers and varying amplitudes.

“The LTC5596 works equally well in a sub-10GHz back-haul microwave link as with a 28GHz version,” said Linear.

Other foreseen applications are in radar, avionics, wireless infrastructure, satellite communications and test gear, operation is from a single 3.3V supply, drawing 30mA nominal, and all pins including the input can withstanding up to 3.5kV (human body model).

As well as the -40 to 125°C H-grade part (which is 100% tested over temperature, and has guaranteed slope and intercept point), there is a -40 to 105°C I grade version. Both come in a 2 x 2mm plastic 8-lead DFN.