Microwave Engineering Europe - November 2008 - (Page 22) 22 MMICs Table 1: Measured performance summary. The conversion loss performance versus LO drive level is plotted in Figure 10 for an LO of 28 GHz and an RF input of 22 GHz. Conversion loss is still reasonable even with an LO drive as low as +5 dBm. As LO drive increases the conversion loss reduces gently. By the time the LO drive is +10 dBm the conversion loss variation is levelling off. The simulated performance (dotted trace) is in good agreement with the measured. Power transfer characteristics of the mixer were measured in both up and downconversion modes. Figure 11 shows the input power versus output power for the three representative devices at an RF of 40 GHz and an LO of 42 GHz (the top of both bands Figure 11: Downcoversion compression characteristics, RF = 40 GHz, LO = 42 GHz. respectively). The input referred 1dB gain compression point (P-1dB) is around +3 dBm. The measured P-1dB at lower LO frequencies increases to around +7 dBm. Similar power transfer characteristics in upconvert mode are plotted in Figure 12. The IF input is 9 GHz and the LO is 36 GHz, resulting in an RF output of 27 GHz. The input referred P-1dB in this case is around +7 dBm. The measured LO to RF rejection is plotted against LO frequency in Figure 13 (strictly speaking the plot shows the LO to RF transmission rather than rejection). The level of rejection is determined by the performance of the on-chip baluns, the symmetry of the IC layout and the matching between devices on the IC. Leakage between the measurement probes can also affect the measurement and care must be taken to ensure that isolation between the probes is adequate. At low LO frequencies the LO to RF rejection is around 40 dB. As may be expected this degrades gradually with frequency to around 27 dB at the top of the LO band (42 GHz). The LO to IF rejection was also measured and found to be greater than 30 dB across the band. 5. Summary and conclusions This paper has presented the design and measured performance of a broadband, passive (bi-directional) mixer MMIC realised on a commercially available PHEMT process. A summary of the measured performance is presented in Table 1. Except where indicated, all measurements were made on-wafer with an LO drive level of +10 dBm. It should be noted that this MMIC design is the property of Elisra Electronic Systems Ltd. 6. References [1] Devlin, Liam “Mixers”, IEE Tutorial Colloquium on “How to Design RF Circuits”, April 5th 2000, pp 9/1-9/20 (available from: http://www.plextek. co.uk/papers/mixers2.pdf). [2] Maas, S.A., “A GaAs MESFET Balanced Mixer with Very Low Intermodulation”, 1987 IEEE MTT Symposium Digest, p895. [3] Devlin, L.M. “The Design of Integrated Switches and Phase Shifters”, Proceedings of the IEE Tutorial Colloquium on “Design of RFICs and MMICs”, Wednesday 24th November 1999, pp 2/1-14. [4] Marchand, N. “Transmission-Line Conversion”, Electronics December 1944, pp 142-145. [5] Devlin, L.M., Dearn, A.W., Pearson, G.A., Beasley, P.D.L and Morgan, G.D. “A Monolithic, 2 to 18 GHz Upconverter”, proceedings of the 2002 IEEE MTT-S. Figure 12: Upconversion compression characteristics, IF = 9 GHz, LO = 36 GHz. Figure 13: LO to RF transmission versus LO frequency. Microwave Engineering Europe ● November 2008 ● www.mwee.com http://www.plextek.co.uk/papers/mixers2.pdf http://www.plextek.co.uk/papers/mixers2.pdf http://www.mwee.com
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