H-Mode mixer - Switches - FSAV450

Fairchild FSAV450

The FSAV450 (QSOP-16 package) contains 4 SPDT switches with a common control line. Only 2 switches are needed to implement the H-Mode mixer. The PCB layout of the FSAV450 with the 3 TT4-1A transformers is very compact indeed. The FSAV450 does not require an 74AC74 divide by two squarer as it does not need both Q and !Q. However in this test the 74AC74 squarer is used.

The following table summarizes the measurements with the FSAV450:

FSAV450 + TT4-1A + 74AC74 Vdd = 5.0V, Vbias = 1.7V Best bias
Band BPF mixer MDS -dBm IF rej spur mixer IIP3 (dBm) @ 20KHz spacing Bias IIP3
IL CL - + avg -6 -3 0 +3 +5 0
-dB -dB BPF BPF -dB dB dBm dBm dBm dBm dBm V dBm
160 3,3 5,08 132 128 32,0 41,7 1,70 41,7
80 1,4 5,04 133 131 31,6 35,7 37,0 39,5 36,7 31,2 1,70 39,5
40 2,3 5,00 133 129 30,4 36,7 1,70 36,7
30 3,4 5,00 133 129 30,4 36,0 1,70 36,0
20 3,4 4,96 133 129 29,2 37,7 1,70 37,7
17 3,0 5,00 133 129 27,6 38,8 1,70 38,8
15 3,9 5,00 133 128 27,2 1,3 37,1 1,75 37,1
12 3,7 5,04 133 129 26,4 33,8 1,80 33,8
10 2,3 5,04 133 129 24,8 32,5 1,70 32,5
6 5,44 131 20,8 26,7 1,90 26,7

The FSAV450 is tested at 5V Vdd with bias at 1,7V. The optimum bias point is found to depend significantly on the input termination of the mixer. A step attenuator set at 0dB before the mixer gives very different results than no step attenuator at all. All mixers that depend on the bias point had this behavior, but the FSAV450 was the worst.

Because of the low bias point voltage, IP3 from +3dBm input level and up is deteriorating rapidly.

Rapidly degrading IP3 with frequency, but considering that this is a 5V device still rather good!

The spur reduction on 15M is rather good.

Like the FSAV430 and FSAV330, the 9MHz RF-IF isolation is not very impressive

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