A Novel Fully Analog Signal Conditioning Circuit for Loss-Less Capacitive Sensor Estimation

In this paper, a novel fully analog signal conditioning circuit for loss-less capacitive sensor estimation has been introduced. The proposed circuit employs a new form of the Wheatstone bridge in order to implement a novel null instrument. In contrast to the conventional ac Wheatstone bridge, all components of the used bridge, except capacitive sensor, are conventional resistors. Therefore, the used bridge is intrinsically unbalanced. In order to balance the bridge, a fully analog feedback network has been used. The main advantage of the proposed circuit over previous null instruments is that, it no longer requires controllable elements such as voltage controlled resistor in order to implement the feedback loop. In the proposed circuit, the bridge is balanced by using a simple and appropriate feedback network which is made by using only an operational amplifier and a resistor. The proposed circuit has been realized only by the use of Op-Amp-based amplifiers and a differential amplifier. Due to the simplicity of the architecture, it can be made by discrete and inexpensive parts. The suggested signal conditioning circuit is excited by a Sine voltage source and the phase difference between output and input voltages depends on the capacitive sensor value. The capacitive sensor estimation can be done by measuring the foresaid phase difference.