Current feedback

Fig. 6.22 Analog circuits for operation of ion-sensitive field-effect transistor (ISFET) (a) in constant applied voltage mode ((6.62) and (6.63)) and (b) in (source-follower) constant current feedback mode ((6.65) and (6.69))...

Lee, Y., Z. Ding, A.J. Bard. 2002. Combined scanning electrochemical/optical microscopy with shear force and current feedback. Anal. Chem. 74 3634-3643. 

Fig. 18 Amplifier with OTA and current feedback (simplified circuit)...

Fig. 19 Frequency response a voltage feedback, b current feedback...

In contrast to common OPAs a low ohmic current source reloads internal parasitic capacitance, which determines the upper cut-off frequency. Consequently a much higher slew rate becomes possible. Gain for both voltage and current feedback OPA circuits is ... 

Current feedback amplifiers always consist of a diamond transistor (DT) and a buffer stage internally connected. The OPA660 [42] or its replacement OPA860 [43] allows separated access to both circuit parts so that a voltage-controlled current source (OTA) at a bandwidth of 90 MHz and a buffer stage at a bandwidth of 700 MHz are available. In contrast to normal transistors the diamond transistor, whose temperature-stabile operating point is internally determined, allows four-quadrant operation. The OTA provides the required almost-ideal transistor to design an emitter-coupled oscillator. 

A servo press is a press machine with a closed-loop control of the position and/or force. Those machines can be operated in a path-driven, force-driven, or energy-driven mode and thus mark a fourth class of press machines. But those machines can only be operated in one of those modes, which is decided by the control system. A path-driven mode in servo presses requires a position feedback loop, a force-driven mode, and a current feedback loop, while the energy-driven mode does not require any feedback loop. 

CHI speed feedback CH2 torque current feedback CHS excitation current feedback CH4 rotor flux angle... 

CHI speed reference CH2 speed feedback CHS torque current feedback CH4 motor flux angle ... 

Figure 19. The waveforms of speed reference, actual speed, torque current feedback, excitation current feedback and flux angle with load...

A potential safety hazard is the fact that with armature current feedback, the armature current is connected to the operator control and potentiometers maybe operated at high potentials (500 V). This problem can be eliminated using isolation transformers or DC to DC chopper circuits. 

In the electrode switching studies, the VCCS was developed with a modified Howland constant-current generator (Figure 30.4) and it was fed by the VCO. The VCCS had two operational amplifier AD811 ICs (Analog Devices Inc., United States) [51]. The AD811 is a high-speed wideband current feedback operational amplifier which is suitably used in modified Howland current source with a feedback resistor [50]. 

In previous sections, we described the conventional op-amp and examined some of its applications. In this section, we survey other important operational elements—the current feedback op-amp (CFB), the operational transconductance amplifier (OTA), and the current conveyor (CC). All of these other operational elements are available commercially, and aU offer advantages and have some disadvantages in comparison with conventional op-amps such as the /xA741. Unlike the conventional op-amp, which is a voltage-controlled voltage source (VCVS) operational element, current is the main variable of interest at either an input or an output port of all the other operational elements. 

Franco, S. 1991. Current-feedback amplifiers. In Analog Circuit Design, ed. J. Williams. Butterworth-Heinemann, Boston. 

Mahattanakul, L, and Toumazou, C. 1996. A theoretical study of the stabihty of high frequency current feedback op-amp integrators. IEEE Trans, on Circuits and Systems I, Vol. 43, No. 1, pp. 2-12. 

Takahashi, Y., Shevchuk, A.I., Novak, P. etcd. (2010) Simultaneous noncontact topography and electrochemical imaging hy SECM/SICM featuring ion current feedback regulation. Journal of the American Chemical Society,132, 10118-10126. 

Garreau, D. Hapiot, P. Saveant, J.M. (1990). Fast cyclic voltammetry at ultramicroelectrodes Current measurement and ohmic drop positive positive feedback compensation by means of current feedback operational amplifiers. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 281,73-83. 

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