Amplifiers evaluation circuits

This example shows an analog solution with a V/I converter. Another possibility is an instrumental amplifier instead of the V/I converter. The analog evaluation circuit is economical relating to wafer-area, but there are a lot of design features necessary for a high accurate signal evaluation. All circuit blocks must be designed to be insensitive to temperature and mechanical stress. 

Further, if within the electrical circuit the ohmic resistance R can be neglected, the ic wave leads to the potential by 90°, as is known, which means that shows a positive 7t/2 phase angle shift ( between tt/2 and zero. Our main objective in AC polarography, however, is the faradaic current, so a separating condenser is placed between the amplifier and normal resistor in order to filter out the d.c. current and to evaluate the ac current component. As we want to understand the relationship between idc(i ) and iac(i ) as a function of Edc and Eac applied, we may consider Fig. 3.41(a) and (b). 

This relation is only valid for acoustically thin films. Concretely, it means that the relation is not respected when thick layers are used because the influence of the viscoelastic properties of the layer may appear in the frequency change. This effect is, in general, amplified when polymer Aims are used. To determine the maximum useful thickness, electroacoustic measurements allowed a pertinent value to be evaluated. In a first step, a classical Butterworth-Van Dyke equivalent circuit of the loaded quartz (Fig. 13a) is extracted... 

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