Hello KlausST,
I really appreciate all the help you've given me so far, and I'm sorry if my previous message came across as dismissive or critical. However, I still have some questions and concerns about the circuit, and I was wondering if we could discuss them further. The circuit block includes a transimpedance amplifier. Normally, a zero-volt bias is achieved by connecting 0V to the anode and the cathode to virtual ground, which is a common op-amp configuration. In this circuit, however, both the anode and cathodes are connected to +5V to achieve zero bias, which is my understanding of the circuit. The transimpedance amplifier output is a DC positive region modulating signal of sine wave. This signal is converted into straight square frequency by a separate op-amp, which can be read by the DSP controller to measure the frequency of the samples. The DSP controller is a key component in processing the signal data. The transimpedance amplifier is then fed into another amplifier stage to prepare the single-ended output for the gain and to be used with the AD7722, which accepts only differential input. To achieve this, other stages of op-amps are used to create a 180-degree out-of-phase signal of the amplified gain, converting the single-ended amplifier output to a differential-ended output, which can then be fed to a differential ADC that is both amplified output can be fed to the differential ADC in phase which is 0 degree and other is 180 out of phase. This ADC communicates with the DSP processor on the SPI bus. Additionally, there are pull-ups of 4.7K connected next to 180K ohm resistors after amplifier outputs and to other amplifier inputs. These are not connected with ordinary relays, but with solid-state analog switches. For the sake of schematic clarity, I drew the standard relay signals. Also, I believe this 4.7K pull-up may be connected because there are two modes of light operation in the machine - the first is the transmission mode, where the light passes through the sample and many IR LEDs are connected across the sample some 15 inches away, and the second is the reflection mode, where only 4 IR LEDs are connected to the sensor itself for when light cannot pass through the sample.
Take pin3 of the AD820.
In the original design clearly shows a capacitor connected to pin 4.
--> Missing in your schematic.
I hope below diagram clarifies.
In the original design there are a lot of connected parts and vias.
--> missing all of them in your design.
This leads to a lot of unconnected parts in your design.
Like:
* resistor from pin4 (right pad)
* All three capacitors left of the 44 pin IC (left pads)
* and so on...
The other parts of the circuits. I hope below diagram clarifies.
Really appreciate your feedback.