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AD8363 resistor divider values for TCM1 and TCM2

Question asked by mallesh on Apr 1, 2018
Latest reply on Apr 5, 2018 by andy_m



My operating frequency range is 4 MHz to 1GHz. 


1. First question (resistor value selection for V_TCM1 and V_TCM2)


Table 4 of datasheet shows that V_TCM1 should be 0.47V and V_TCM2 should be 1.0V. Also, I see that the input impedance of TCM1 is 5k Ohms and TCM2 is 500k Ohms. 


Vref is 2.3V with maximum current source of 4mA.


So, accounting for input impedance, can I use R17 as 1k Ohm and R18 as 3.3kOhm (refer to Fig 57). With this V_TCM1 will be 2.3/(833.33+3300)*833.33 = 0.4657V. 


For V_TCM2, can I use R12 as 22k and R9 as 27k? 


These resistor values make sure that source current from Vref is less than 1mA. 


2. Selection of Clpf. Can I use 4.7nF? I would like to keep rise time and fall time as low as possible. I am fine with ripple of 100 mV as I can average it out in my software. 


3. Can I keep Chpf open?


4. Can I use zener BZX84C3V3ET1G to limit o/p voltage to 3.3V? My aim is to detect the power levels below 0 dBm. If by any chance it goes above that, I would like to clip. I see that Vout has a capability source 10 mA current. I am just wondering if I need to introduce a resistor between zener and the V_out.


V_out is connected to SAR ADC input. 


Please let me know.