I am building a circuit in which an analog signal ( sine wave) of around 25 mV leaves the main pcb board to a second module pcb through an HDMI cable. Inside the HDMI cable, I am using one of the twisted pair for my signal. One wire of the twisted pair carries the signal on its outgoing path from main pcb to module pcb, and the other wire of the twisted pair carries the signal on its incoming path from module pcb to main pcb. On the module I have an unknown Impedance which I want to measure. The 25mV signal of a known frequency is generated by an IC on the main board. It then passes through the unknown impedance on the module pcb and returns back to the IC on the main board which then calculates the Impedance. I want to measure the impedance for a range of frequency from 100 Hz to 100 KHz.
1) I am using a double shielded HDMI cable and the shield I have connected to ground. My 25mV analog signal has a DC bias of 2 V. The shield will protect the signal from external ac noise signals but will there be a capacitance between my shield and signal which could be a source of error in my system? Should I connect my shield to 2 V?
2) Error in my results in the range of frequencies from 25 KHz to 100 KHz increases with increased error for a higher frequency. I am not able to understand whether this is due to ineffective shielding of my signal?
I have attached a simple drawing indicating the path of signal. I am looking for some guidance regarding my questions. Thank you.
1) I am using a double shielded HDMI cable and the shield I have connected to ground. My 25mV analog signal has a DC bias of 2 V. The shield will protect the signal from external ac noise signals but will there be a capacitance between my shield and signal which could be a source of error in my system? Should I connect my shield to 2 V?
2) Error in my results in the range of frequencies from 25 KHz to 100 KHz increases with increased error for a higher frequency. I am not able to understand whether this is due to ineffective shielding of my signal?
I have attached a simple drawing indicating the path of signal. I am looking for some guidance regarding my questions. Thank you.
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