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# Help need in analog circuit design to get phase and amplitude.

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#### veerubiji

##### Full Member level 2
Hi,
I am generating sine signal with 125 KHz using micro controller and giving it to Capacitive(cylindrical shape) sensor. If the sensor out is low to read then i am using two amplification stages to increase signal amplitude. I am using multiplexer to select best signal from sensor out. The out signal also 125 KHz but there is a phase shift in the signal based on medium between electrodes.

Now I want to calculate phase shift between two signals(vg and vr) as well as both signal amplitude. I am confusing which circuit will gives max amplitude of both signals and phase shift between two signals? I am able to read phase shift and amplitude of both signals using micro controller. I can use ADC to read amplitudes but i am worrying about phase shift.?

I am attaching simple block diagram of my circuit as shown below.

Any suggestions which circuit will gives phase shift as well as amplitude of input and output?

Phase shift can be done by using comparators to generate a square-wave at the zero crossing point of each signal, measuring the time difference between the two square-waves and then calculating the phase shift from that based upon the frequency of the signal.

I am not sure it is the solution you are looking for but the AD8302 will measure phase and amplitude. While it works up to 2.7GHz, it also works at low frequencies as well - I have used it well below 1MHz. Not cheap though.

Keith

A general way to measure vectorial signals is based on vectorial/quadrature demodulation. That's the method e.g. used in most VNA. In can be either implemented as a homodyne demodulation with quadrature reference signals or as heterodyne demodulator with frequency offset.

alexan_e

### alexan_e

Points: 2
I am not sure it is the solution you are looking for but the AD8302 will measure phase and amplitude. While it works up to 2.7GHz, it also works at low frequencies as well - I have used it well below 1MHz. Not cheap though.

Keith

I have read the datasheet, it will give amplitude as a ratio of input /output. I am worrying about phase shift, the phase shift between two signals what i have is not more than 90. Is it give accurate phase shift between two signals(input/output).

The specification is better than 1 degree. I have used them at low (375kHz) and high frequencies (300MHz) with sine waves of widely differing amplitude. They can be quite useful.

Keith

The specification is better than 1 degree. I have used them at low (375kHz) and high frequencies (300MHz) with sine waves of widely differing amplitude. They can be quite useful.

Keith

Hi Keith,

Can use it to design an smps dc-dc converter frequency response analyser

keith1200rs: Do you know if this chip will perform well as low as 3kHz? or even down to 100Hz?

Provided you use appropriate capacitors externally (e.g. to the OFSA/OFSB/PFLT/MFLT pins) it should work at very low frequencies. I assume it is DC coupled internally.

Keith.

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