Integrated wideband passive mixers support wideband operation for wireless infrastructure and software-defined radio applications
The devices enable multiband, single-board receiver designs by combining a wideband LO (local oscillator) amplifier, a programmable RF balun, a high-linearity mixer core, a programmable IF filter, and an IF amplifier.
These passive mixers extend across a 700-MHz to 2800-MHz frequency range in a single device while delivering input IP3 (third order intercept) of 24 dBm, an 11 dB SSB noise figure and 7 dB of power conversion gain. These performance specifications are maintained across the full operating frequency range. Both the ADL5811 and ADL5812 passive mixers are designed for wideband wireless infrastructure applications and software-defined radio applications, including multi-band/multi-standard cellular base station receivers, wideband radio link down converters, multi-mode cellular repeaters, and picocells applications.
“Wireless receiver designers typically have had to choose between an active mixer, which offers excellent wideband operation and moderate spurious-free dynamic range, or a passive mixer, which has greater SFDR performance but much narrower operating bandwidth,” said Peter Real, vice president, Linear and RF products, Analog Devices. “The ADL5811 and ADL5812 passive mixers eliminate the need for this trade off by giving engineers the linearity, distortion and noise performance they need while also supporting true wideband frequency operation.”
The high performance across 700 MHz to 2800 MHz of the new passive mixers is the result of three technical advances, most significantly the development of a limiting LO amplifier capable of generating a high-voltage, fast-rise-time, square wave over a wide bandwidth with no DC current penalty compared to existing narrow band mixers.
The second technique involves the integration of a tuned,RF balun structure to ensure a well-balanced RF signal is applied to the FET mixer. Previously, narrowband mixers incorporated an RF balun consisting of a magnetic or transmission line transformer, which provided low loss but only moderate bandwidth.
A third technique addresses the potential for the passive mixer’s structure to generate a composite signal that could result in the early compression of the IF amplifier. ADI reduced the amplitude of the unwanted sideband into a load by designing a tuned filter network to provide the proper sum termination as a function of the RF and LO frequencies.
The frequencies of the ADL5811 and ADL5812 can be easily changed using a three-wire SPI (serial port interface), which allows designers to tune the mixers with no need for external impedance matching components. Performance can be further optimized by digitally adjusting the DC bias voltage to the passive mixer gates. To minimize power dissipation, each channel of the dual-channel ADL5812 can be enabled or disabled independent of the other. For DPD (digital pre-distortion) transmit observation receivers or non-diversity applications, the single-channel ADL5811 can implement a single receiver chain in a multi-channel or multi-band platform.
In summary the ADL5811 and ADL5812 passive mixers feature:
- Limiting LO amplifier with wide bandwidth;
- Tuned RF balun structure to ensure well balanced RF signal;
- Tuned IF filter network that provides proper sum frequency termination;
- Single ended, 50-Ohm input matched for the RF and LO input;
- Wideband 700-MHz to 2800-MHz frequency range;
- Input IP3 of 24 dBm;
- SSB Noise figure of 11 dB; and
- Power conversion gain of 7 dB.
As part of a complete wireless communications signal chain, the ADL5811 and ADL5812 passive mixers can be designed together with the company’s AD8375/6 IF DGA or ADL5561/2 differential amplifier and the ADF435X series of synthesizers for a complete receiver signal chain.
For further information: www.analog.com/rf.
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