Differential input amplifier

DifTerential amplifier. An operational amplifier with two inputs of opposite-gain polarity with respect to its output. Differential-output amplifiers can also have two opposite-sense outputs. 

Microdielectrometry was introduced as a research method in 1981 14 and became commercially available in 1983 20). The microdielectrometry instrumentation combines the pair of field-effect transistors on the sensor chip (see Sect. 2.2.3) with external electronics to measure the transfer function H(co) of Eq. (2-18). Because the transistors on the sensor chip function as the input amplifier to the meter, cable admittance and shielding problems are greatly reduced. In addition, the use of a charge measurement rather than the admittance measurement allows the measurements to be made at arbitrarily low frequencies. As a matter of practice, reaction rates in cure studies limits the lowest useful frequency to about 0.1 Hz however, pre-cure or post-cure studies can be made to as low as 0.005 Hz. Finally, the differential connection used for the two transistors provides first-order cancellation of the effects of temperature and pressure on the transistor operation. The devices can be used for cure measurements to 300 °C, and at pressures to 200 psi. 

The method is schematically illustrated in figure 2. The operational amplifier A, working in the follower configuration, is used to apply, between the points D and T, the potential difference V present at the terminals of the generator G, which is assumed to be positive. This hypothesis simplifies the analytic expression of the potential difference V, because its polarity determines the behaviour of the two electrodes. The differential-input voltmeter Q determines the intensity of the current that, flowing through the electrochemical cell C from D to T, polarizes the electrodes Wi and W. These electrodes, made of the same material, are identical. Their surface areas are equal to S and, conventionally, they are polarized anodically and cathodically. 

The functionalized gold electrode and the reference electrode were connected to the amplifier differential inputs (see Fig. 3.6). The amplifier output voltage, equal to the open-circuit potential for... 

Figure 8.13 (a) Differential (instrumentation amplifier) input, (b) Single-ended input, (c) Common mode coupled input, (d) Symbols for ground and local reference. 

The electric potential between the vacuole of an internodal cell and the bathing solution was measured by using glass microelectrodes (approx. 10 pm tip diameter) filled with a 3 mM KCl solution (pH=2), using a WPI (Model 750) amplifier with a differential input,... 

Differential input An amplifier input in which the signal is applied two complementary terminals that are not referenced to ground. 

Differential dc The maximum dc voltage that can be applied between the differential inputs of an amplifier while maintaining linear operation. 

Figure 12.5 Common mode rejection device using the differential input of an amplifier...

Figure 7.26. Operational amplifier in differential input mode.

One additional point needs to be considered. The commercial DSC is constructed in a slightly different fashion than that just described. Rather than letting the differential amplifier loop correct only the temperature of the sample, an equal amount of power is subtracted from or added to the power delivered to the reference by the average temperature amplifier. This is accomplished by proper phasing of the power input of the differential temperature amplifier. In reality, thus, one-half of is added to the sample calorimeter in addition to the full power from the average temperature loop, while one-half of IFp is at the same time subtracted from the power going into the reference calorimeter. This results in a total additional power to the sample that is equal to IV, as required by our calculations. The performance of the DSC is thus still described by Eqs. (1), (4), (5), (10), and (11). 

---