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Question about input stage of ADC 9467 @ 140MHz

Question asked by Renan on May 31, 2012
Latest reply on Jun 6, 2012 by UmeshJ

Hello, I am currently working on acquisition board with ADC 9467. I have some troubles regarding the input stage of this ADC. In fact i followed datasheet recommendations and now when i measure SWR and S11 results are nor good. ADS seem to work as switched capacitor network. Attached you can find schematic and results with network analyzer. SWR A is SWR with L2 and L3 removed and R3=R6 = 51 ohms LOG A is S11 with L2 and L3 removed and R3=R6 = 51 ohms As soon as i connect L2 and L3 and R3=R6 = 33 Ohms, SWR = 2.38 @ 140MHz and S11 is -6dB If R3=R6 = 150 ohms with L2 and L3 connected, SWR = 1.6 @ 140MHz and 2 @ 170MHz and S11 = -10dB Frequency is 140 MHz centred with BW of 65Mhz. Nominal value is 0dBm. I would like to match with input 50 Ohms and SWR should be <1.5 Do you have any idea to help me to match this input stage? Many thanks Renan