Demodulator supports 5G wireless

Designed with more than 1GHz, -1dB flatness bandwidth, the LTC5586 supports next-generation 5G wireless infrastructure equipment such as digital pre-distortion correction receivers for basestations, microwave backhaul and software-defined radios (SDR), as well as other broadband receiver applications.

The high linearity I/Q demodulator, from Linear Technology, has an input port that is truly broadband, say the company. With a single network, it is 50Ohm matched from 500MHz to 6GHz, covering all the LTE bands as well as the emerging 4.5G and 5G bands at 3.6 and 5GHz. For operation from 300 to 500MHz, an additional capacitor is all that is required. The device also has built-in SPI tunability, allowing the demodulator to set its LO input to any frequency band from 300MHz to 6GHz with no external matching components. It supports very high OIP2 of 80dBm and 60dBc sideband suppression, for receiver performance.

The true zero-IF design demodulates wideband RF signals directly to baseband DC or low IF coupling. The demodulator exploits the quadrature relationship between the two I and Q channels, containing all the information available when both channels are sampled at one-half the bandwidth of the full RF bandwidth from which they came. As a result, the ADCs’ sampling rate and cost can be reduced.

An RF switch selects one of its two inputs to a programmable attenuator via the on-chip serial bus. This front end attenuator has a gain control range of 31dB in 1dB steps, allowing the receiver to accommodate a wide range of signal inputs. The demodulator consists of I and Q mixers, with respective LO driven by an accurate wideband quadrature phase shifter. After the signal is demodulated, two programmable gain amplifiers provide gains to the I and Q baseband signal paths. Maximum gain of 7.7dB can be set by the serial port in 1dB steps, allowing users to optimally set the signal levels while driving a pair of external A/D converters directly.

On-chip tuning facility for simple calibration is via the SPI serial port to adjust the I and Q amplitude and phase balance. The company claims calibration can attain unprecedented 60dBc or better image rejection performance. The same interface can optimise the IIP2, IIP3, HD2 (2nd harmonic distortion) and HD3 performance, to improve overall linearity performance of a receiver. With the device’s baseband DC coupled, its DC offset voltage can be zeroed, including the entire baseband signal chain, so long as the combined total offset is within the adjustment range of the device.

The LTC5586 comes in a 5.0 x 5.0mm plastic QFN package. The I and Q outputs are able to drive directly into a pair of interstage filters and external ADCs when terminated externally with a 100Ohm differential impedance.

Operating temperature range is specified from 40 to 105 degree C case.


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