Hi everybody,
I have a problem regarding the gain of TDC1000. I am checking the gains of LNA and PGA of TDC1000 by bypassing one them and checking the peak COMPIN pin voltage and echo voltage on the receiver sensor. I have set everything for 200khz signal. Here are the gains I observed ;
LNA bypassed, PGA is set to 21dB: Vout/Vin = 2.5
PGA bypassed, LNA is set to 20dB by resistor: Vout / Vin = 4.5
Note that the above numbers are NOT in dB, they are just ratios of output and input voltages.
1- I have a GASEVM board and I checked the gain of LNA and PGA by the same way(bypass one of them check the max COMPIN voltage and signal on receiver sensor) and observed slightly larger values but still not even close to 20dB on LNA and 21dB on PGA(I did not write down the gain values so I am not able to give the exact numbers for the gains onGASEVM board). Can you please explain why I don't observe 20dB on LNA and 21dB on PGA on both my own board and GASEVM ?
2- I have checked the datasheet of TDC1000. Page 10 figure 8 gives "LNA Gain vs Frequency" plot but it is only given for capacitive feedback mode. I am using resistive feedback mode. Why there is no data for resistive feedback mode ? Can you please explain/show how LNA and PGA would behave in resistive feedback mode ?
3- Can you please tell me how would LNA and PGA behave for different VDD voltages. I am using 2.8V supply on VDD(1.4V VCOM) and wondering what would happen in I increase VDD to 4V(and so does VCOM to 2V) ? As can be seen on the datasheet, non-inveting input of LNA is tied to VCOM and I would like to understand the effect of different VCOM values on overall gain of LNA and PGA.
Many thanks
