Using PGAs for sensor signal | Cypress Semiconductor
Using PGAs for sensor signal
I want to connect a radar sensor to a 5LP. The output signal will be a (more or less) sinusoidal signal, where the frequency determines the speed of the object, the amplitude reflects how much energy is reflected by a given object.
The application note for the sensor states that an amplifier circuit with a gain of ~70-80dB (~3100 to 10k) should be used (. The reference circuit uses two amplifier stages with gains of 100 and 45, so total gain is 4500. The stages are implemented as low pass filters. Input to the circuit and connection between the amplifier stages is AC coupled.
Now, I wonder how to implement the amplifier effectively with the 5LP's internal programmable gain OpAmps. My goal is to feed the signal into a ADC and run a FFT over it. I want to use the PGAs to avoid saturation if something is really close to the sensor, so I can reduce the gain.
Maximum gain of a PSoC 5LP PGA is 50, so I'd use three of them to get into the 10k range from the reference circuit. So, the first question is about connecting the PGAs: the reference circuit amplifiers are fed by the inverting input, and the non-inverting input is kept on VDD/2. The PGA circuit symbol of PSoC seems to use the non-inverting input as signal source (Vin) and the inverting input for the reference voltage (Vref), reflecting a non-inverting amplifier opposite to the reference circuit. Are there any disadvantages to be expected?
Second question: I'll keep the AC coupling between the PGAs by external capacitors, but I think I can skip the capacitors used for low-pass filtering (capacitor between OpAmp output and input) and make the LPF by software, would this work?