Mixer for instrumentation

Test instrumentation may need to accommodate signals having a wide percentage frequency bandwidth. For easy processing of these RF signals, the input can be up-converted to reduce the percentage bandwidth.

To help with this, Mini-Circuits has developed a high-performance passive mixer that allows original-equipment manufacturers to optimise receiver design.

The company's SIM-U742MH+ mixer is based on a combination of low-temperature-cofired-ceramic (LTCC) technology, semiconductor technology and a highly-manufacturable circuit layout. The combination results in a small device with high insensitivity to electrostatic discharge and good temperature stability.

The device is built on an LTCC substrate, suitable for designs with multilayer circuits. In contrast to conventional planar circuit designs, in which all circuit elements are placed on one side of a single-layer printed circuit board, LTCC circuits can be designed and fabricated in three dimensions, even with embedded components between layers, to save space.

This results in a mixer that is smaller than some commercial semiconductor-based mixers. While the mixer incorporates semiconductors to accomplish its frequency-translation function, it is a passive design that operates without DC bias.

The mixer is double-balanced, built around a diode quad. Except for the diodes, the entire structure is in multiple layers of LTCC which is inherently hermetic.

By integrating components in LTCC, the mass of the mixer is minimised, making it rugged in terms of withstanding shock and vibration.

The mixer accepts IF signals from 50 to 2200 MHz and local-oscillator signals from 4100 to 7400 MHz and a nominal level of +13 dBm to produce RF output signals from 3900 to 4300 MHz.

It performs the frequency upconversion with a typical conversion loss of 8.0 dB. The conversion loss increases with IF frequency.

The double-balanced mixer features typical LO port VSWR of 3.5 to 8.5 dB. The return loss measured at the RF port is 5.5 dB typical, while the return loss at the IF port is typically within 5 to 30 dB across the full IF band.

The mixer supports conventional surface-mount applications.