60dB Sideband Suppression, Ultra-Wideband 6GHz Zero-IF I/Q Demodulator Launched

Linear Technology Korea (CEO Hong Sa-gwak) has announced the launch of a new high-linearity I/Q demodulator product (model: LTC5586) featuring over 1GHz bandwidth with –1dB flatness.

This product supports next-generation 5G wireless infrastructure equipment such as base stations, microwave backhaul, and digital predistortion correction (DPD) for software-defined radios (SDR), as well as other broadband receiver applications.

The LTC5586 provides a broadband RF input port. Using a single matching network, the product is matched to 50Ω in the 500MHz to 6GHz range and covers all LTE bands as well as newly emerging 3.6GHz and 5GHz 4.5G and 5G bands. To support operation in the 300MHz to 500MHz range, additional capacitors are required.

The device features built-in SPI-adjustable tuning capability, allowing the demodulator to set the LO input across the frequency range of 300MHz to 6GHz without external matching components. The new demodulator supports very high OIP2 of 80dBm and 60dBc sideband suppression, ensuring excellent receiver performance.

The LTC5586 is a true zero-IF design that directly demodulates broadband RF signals to baseband DC or low-IF coupling. The demodulator leverages the quadrature relationship between the two I and Q channels, and when both channels are sampled across a bandwidth equivalent to half the entire incoming RF bandwidth, all available information is fully captured. As a result, sampling rate and cost of the A/D converter (ADC) can be reduced.

At the front end, the LTC5586 features an RF switch selecting one of two inputs with an attenuator programmable through an on-chip serial bus. This front-end attenuator provides 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, each driven by its respective LO with a precise wideband quadrature phase shifter.

After signal demodulation, two programmable gain amplifiers provide gain to the I and Q baseband signal paths. Maximum gain of 7.7dB can be set through the serial port in 1dB steps, and the device can directly drive a pair of external A/D converters while the user optimally sets signal levels.

Additionally, the LTC5586 features proprietary on-chip tuning capability for simple calibration through the SPI serial port. Through this interface, users can adjust I and Q amplitude and phase balance, resulting in significantly simplified calibration that achieves excellent 60dB or better image rejection performance. The same interface can optimize IIP2, IIP3, HD2 (2nd harmonic distortion), and HD3 performance, improving overall linearity performance of the receiver. Since the device's baseband is DC-coupled, the DC offset voltage of this product can be zeroed across the entire baseband signal chain. The integrated total offset that is possible for as long as practical exists within the tuning range of the LTC5586.

The LTC5586 is supplied in a 5mm x 5mm plastic QFN package. The I and Q outputs feature 100Ω differential impedance and can directly drive a pair of interstage filters and external ADCs when terminated externally. This enables a compact solution with minimal external components required. The operating temperature range is specified from –40°C to 105°C. The LTC5586 is supplied at $7.79 per unit based on quantities of 1,000 pieces and is currently available in production volumes.