New-Tech Europe Magazine | April 2017

Test & Measurement Special Edition

intermodulation products at some level which can interact with neighboring elements in the RF chain. Since these neighboring elements in real-world systems are often filters, out-of-band signals are fully reflected back into the mixer where they produce a secondary set of spurious signals, which additionally limit the dynamic range of the system. This has been a longstanding problem in RF systemdesign, against which designers were more or less helpless until recently. Various techniques have been employed to compensate forthe adverse effects of stopband reflections (inserting attenuators or isolation amplifiers around the mixer, for example), but these solutions still degrade system SNR and dynamic range, which becomes self-defeating. The results presented in this article demonstrate how reflectionless filters may be used with mixers in up-converter and down-converter configuration to absorb those out-of-band signals within the filter circuit itself. In comparison to conventional filters in the same circuit, reflectionless filters achievesignificant reduction of third order intermodulation products, which corresponds to proportional improvement in system dynamic range. Mini-Circuits offers a wide range of reflectionless filters from stock in tiny QFN packages and bare die form, including low pass, band pass and high pass models with passbands from DC to 30 GHz. These patented products give designers a new tool to achieveperformance improvements similar to those presented here in their own systems.

Figure 2. Top-level schematic diagram of the receiving circuit

Table 3: Summary of Test Conditions for Two-Tone Intermodulation Test in Downconverter Configuration FILTER POSITIONS • Case 1: NO FILTERS • Case 2: REFLECTIVE FILTERS (VARIOUS) on RF and IF PORTS • Case 3: REFLECTIONLESS FILTERS on RF and IF PORTS RF INPUT 800 MHz 2200 MHz TONES TWO TONES SPACING: 1 MHz (800 MHz AND 801 MHz); (2200 MHz AND 2201 MHz)

MIXERS TESTED

•ADE-10H+ •SYM-30DHW+

LUMPED ELEMENT (Sharp Filters)

SLP-1000

IF SLP-1200+ SLP-2400+ SLP-2950+ LTCC FILTERS (Shallow Slope) VLF-1000+ VLF-2250+ VLF-2500+ REFLECTIONLESS FILTERS VLF-800+ IF

RF

SLP-150+

FILTERS TESTED

RF

VLF-160+

XLF-861+ XLF-122+ XLF-252+

RF

IF

XLF-151+

New-Tech Magazine Europe l 55