Signal Processing

Flexible software controlled signal conditioning in analog domain

» Posted on 22. Jul 2012

 

 

Sensor Signal Conditioning

To achieve high performances in processing analog signals in digital systems it is very helpful to be able to condition the analog input signal before interfacing the analog-to digital converter (ADC).

In the software the basic capabilities needed  to reach this goal are:

  • flexible gain
  • setting a DC offset
  • compensating zero offset error
  • compensating temperature drifting

In the hardware a simple anti aliasing filter should guarantee that the input signal is free of frequencies above half of  the ADC’S sampling rate (Nyquist theorem). Additionally the input signal should be translated into a differential signal for driving a real differential ADC for lower system noise impact.

The block diagram above shows a design approach how such a system can be realized. The first element on the signal path is the switch S1, which allows the system to disconnect the input signal and ground the input to compensate zero offset errors given in the system.

The next element on the signal path is the DC biasing of the input signal, which is normally half of the ADC’s input voltage range. Setting the biasing voltage to another value than mid range voltage, will result into a DC-Offset of the input signal if needed by an application.

On the way to the ADC, the input signal may be pre-amplified or not controlling the switch S2 by the software. The pre-amplifer applies a fix gain of +24dB to the input signal making the input even sensible for very weak/small sensor signals. The main amplifier stage is gain controlled by the software and allows to set any gain between -3dB to +18dB.

As a result the introduced block diagram is able to modify the unconditioned signal as shown in the graph above, to an optimized signal covering the whole ADC dynamic range for best performance prepared in the analog domain before the ADC. 

Additional temperature drifting compensations and other calibrations can be realized software driven having above capabilities in the system.

The ACU1 and ACU3 modules designed by ANSARI have the above explained signal conditioning feature already implemented.

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