Inverter, current feedback

Figure 4-219 shows the schematic diagram of a servo-controlled inverted pendular dual-axis accelerometer. A pendulum mounted on a flexible suspension can oscillate in the direction of the arrows. Its position is identified by two detectors acting on feedback windings used to keep the pendulum in the median position. The current required to achieve this is proportional to the force ma, and hence to a. ... 

We have already noted that a negligibly small voltage differential at the inputs will drive a practical amplifier to its limit thus we almost never use the amplifier to deal with an input signal without elaboration of the circuit. Normally the amplifier is stabilized by feeding back part of its output to the inverting input. The manner in which the feedback is accomplished determines the operational properties of the whole circuit. Here our concern is with circuits involving the routing of a current from the output to the input (1-7). 

Commercial electrochemical instruments that measure currents down to 1 pA are available. To reach the nA and pA current ranges, conventional electrochemical instruments frequently are used in concert with a current amplifier, which is a module consisting of a current follower and an inverter (Figure 15.7.1). This device is placed between the working electrode and the corresponding lead from the potentiostat (which usually is the input to another current follower, CF) (19). The amplification factor is Rf/Ro, where Rf is the feedback resistance of the first amplifier and Rq is the output resistance (to CF). 

A current source is connected between the inverting input and the noninverting input. The noninverting input is connected to common. A feedback resistor R, is connected from the output to the inverting input. 

CFBs can be used to reaHze inverting and noninverting amplifiers, current-to-voltage and voltage-to-current converters, and summing and differencing amplifiers. Thus, they can be utilized in a variety of active filters such as Sallen-Key active filters. However, careful stability analysis must be performed for circuits in which CFBs have reactive components in their feedback networks. For example, the usual Miller... 

Operational amplifier 2 in Figure 3-15b is simply a voltage follower, which hits been inserted into the feedback loop of operational amplifier 1. A voltage follower used in this configuration is often called a non-inverting booster amplifier because it can provide the relatively large current that may be required from the amperostat. 

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