Noninverting amplifier

Reference electrode (RE) and potentiostatic setpoint are fed to the inverting and noninverting input of an operational amplifier. The counter-electrode (CE) is connected to the output of the operational amplifier. I (EC) electrochemical current. 

The reference electrode (RE) is connected to the inverting input of an operational amplifier (for example Texas Instruments TL 074), and the setpoint is applied between ground and the noninverting input of the operational amplifier. For electronic reasons Equation 6.2-1 applies. 

The coaxial cable is the major source of noise for yet another reason. At the input of the op-amp, there is always a small voltage noise, which is amplified by the op-amp and appears at the output end. To make a simplified analysis, let the input noise be represented by an ac source at the noninverting input end. The output voltage is (see Fig. 11.3)... 

Fig. H.I. Two simple applications of the op-amp. (a) An inverting amplifier, (b) A noninverting amplifier.

In the noninverting amplifier, the condition of zero difference between the inputs requires Va = Vm- Thus,... 

The frequency is fixed at 50 kHz, with a 50% duty cycle. The noninverting terminal of the error amplifier is tied to the reference voltage (5.1V) and the inverting terminal is tied to ground, so that the oscillator controls the pulse termination. The output signal appears at Aout (pin 11). 

There are several other methods of achieving stability in potentiostatic circuits. A capacitor may be added between the counter and reference electrodes to reduce phase shift in the critical frequency region. Some caution must be exercised since a low-resistance reference electrode then becomes the counterelectrode at high frequencies. A particularly interesting method is known as input lead-lag compensation a series RC is connected between the input terminals of the control amplifier, and a second resistor is connected between the noninverting input and common. This form of compensation has minimum effect on the slew rate of the control amplifier. Further details can be found in the book by Stout and Kaufman listed in the bibliography. 

If amplification of a small input voltage is desired, either of the circuits shown in Fig. 66 and 6c can be used. In the latter case, the noninverting input is grounded and the amplifier acts to hold the inverting (—) terminal at a virtual ground, i.e., = 0. (Actu-... 

For the purpose of this text, an operational amplifier consists of a series of solid-state components designed to have certain fimctional characteristics. A schematic representation of an operational amplifier, given in Figure 6.1(a), shows 5 leads attached to the operational amplifier. The vertical leads, marked Vs+ and Vs-, provide power to the amplifier and are connected to a direct-current power supply. The two leads on the left, termed the noninverting (-I-) and the inverting (—) input, have potentials V+ and VL, respectively. The output potential is Vq. 

The output potential Vq has the opposite sign as the input potential V. A noninverting amplifier is presented in Problem 6.3. 

Show that the output potential for the noninverting amplifier shown in Figure 6.9 can be expressed as... 

The two input terminals are labeled with signs in the manner depicted there. The top one is called the inverting input and the bottom one is the noninverting input. The fundamental property of the amplifier is that the output, e, is the inverted, amplified voltage difference e, where e is the voltage of the inverting input with respect to the noninverting input. That is. 

Recall that in the noninverting configuration, the operational amplifier works to keep F and Rj equal and that the cell current is supplied by the operational amplifier to maintain this condition. If wc consider the path between the inverting input and the circuit comniim at the output, we see that... 

An essential component of modem electrochemical instmmentation is the operational amplifier (OA or op amp) [1]. An OA is a high-gain differential amplifier with an output voltage (Vq) proportional to the difference between noninverting (V+) and inverting (T ) inputs... 

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