Microwave Engineering Europe - November 2008 - (Page 20) 20 MMICs Figure 4: Simulated RF to IF downconversion loss versus LO, RF fixed at 19.6 GHz. MMIC in downconvert mode is plotted in Figure 4. For this simulation the RF frequency was fixed at 19.6 GHz and the LO swept from 20 to 36 GHz (resulting in an IF output of between 0.4 GHz and 16.4 GHz). The red trace represents an LO power of +10 dBm and the blue trace an LO power of +13 dBm. For an LO drive of +10 dBm the simulated conversion loss varies between 8.4 dB and 9.7 dB across the band. A simulation of the conversion loss in upconvert mode is plotted in Figure 5. In this case LO frequency is fixed at 23.5 GHz with a swept IF. As with the downconvert simulation the red trace represents an LO drive level of +10 dBm and the blue trace an LO drive level of +13 dBm. For an LO drive of +10 dBm the simulated conversion loss varies between 7.6 dB and 8.5 dB across the band. 3. Realisation The MMIC was fabricated on the PP15-20, 0.15 mm gate length PHEMT process of WIN Semiconductor. A photograph of one of the mixer MMICs, whilst under RF On Wafer (RFOW) test, is shown in Figure 6. The single ended RF port is on the top side of the photograph and the single ended LO port is on the bottom side. These two ports can be seen interfacing to GroundSignal-Ground (GSG) RFOW probes. The differential IF ports to the right interface to differential G-S-G-S-G RFOW probes for test. The DC probes to the left are for application of the -5 V bias and monitoring of various voltages generated by the on-chip active bias network. The mixer itself requires only a -5 V supply as the gate bias potential for the mixing transistors is generated by the on-chip active bias network. 4. Measured performance The possible permutations of measurement that could be presented for a broadband frequency-converting component are extensive. A limited subset of the actual measurements made is necessarily presented here. The data selected attempts to provide adequate representation of most aspects of the mixer’s performance. However, some features that may be of interest to certain Figure 5: Simulated IF to RF upconversion loss versus IF, LO fixed at 23.5 GHz. Figure 7: RF to IF downconversion loss versus RF, LO fixed at 28 GHz. Figure 8: IF to RF upconversion loss versus IF frequency, LO fixed at 36 GHz Figure 6: Photograph of the mixer MMIC. Microwave Engineering Europe ● November 2008 ● www.mwee.com http://www.mwee.com
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