The PCB design REVISITED one year after

Still not satisfied with the analogue output to the microcontroller of the PCB Rev 7.0 am working on PCB Rev 8.0.  The main reasons for this decision,

1. The Analogue signal is not clean enough, I mixed the digital and analog grounds on the layout Rev 7.0
2. The use of 2 seperate 'pi' filters to stabilise the power to the microcontroller and quad-Op-Amp
3. The circuit will consist of 3 Non-Inverting OpAmps. The first two OpAmps will have fixed gains of 22 and 38.  The last OpAmp will have a variable gain of either 1 or 11 which will be set or driven by an I/O pin refer to this link under under the section Adaptive Amplifier with increasing Amplification during Echo waiting Time.  On the Microchip controllers this is done by turning the I/O pin into Analog and setting it to output to activate the resistor connected to the OpAmp.
4. The use of a voltage clipper circuit to prevent overloading the analog output during the PWM pulse, by the limiting properties of having 2 diodes connected to the ground in opposit directions.  It will be found between the output of the 2nd OpAmp and the input of the third OpAmp.