Bandwidth, operational amplifiers

Amplifier bandwidth. The range of signal frequencies over which an amplifier is capable of undistorted or unattenuated transmission. An operational amplifier should transmit DC voltage accurately the upper (bandwidth) limit is defined as the 3-dB point (attenuation factor of two). Because bandwidth can vary with gain, the product of gain x bandwidth can be a more useful parameter. 

An additional consideration is the gain-bandwidth product specification of the operational amplifier used as the error amplifier. If the Bode character-... 

In this section we will use PSpice to determine the gain and bandwidth of an operational amplifier with negative feedback. Wire the circuit shown below ... 

A simple form of such a circuit is shown in Fig. 3. It uses a low noise operational amplifier and a feedback resistor (Rfb) with a typical impedance of R = 100 MQ. To get a maximum signal-to-noise ratio the bandwidth should be maximized while the noise should be as small as possible. 

The bandwidth of the complete circuit is limited by the bandwidth of the operational amplifier and the parasitic capacitance of Rfb, while the main noise source is given by the Johnson noise density n rb of the resistor Rfb ... 

The characteristics of present amplifiers are such that one can easily obtain accurate, reliable performance on time scales of 10 piS or greater (i.e., bandwidths less than 100 kHz). Time scales below 10 )ns (bandwidths above 100 kHz) can be reached with care in circuit design and choice of components. Building reliable operational amplifier circuits like those described below for time scales under 3 )ns is very difficult. 

In Section 3B-4 we discussed the relationship between the rise time and the bandwidth of an operational amplifier. These variables are also u.sed to characterize the capability of complete instruments to transduce and transmit informaliim, because... 

Note BW bandwidth CMRR common-mode rejection ratio op-amps operational amplifiers. 

The properties of the I-U converter will depend on the correct choice of the operational amplifier. A low noise amplifier has to be used in order to minimize the contribution of the amplifier itself to the background noise. On the other hand, the working bandwidth of the operational amplifier must be high enough to achieve a good time resolution in the control of potential in the patch pipette. 

During the late 1970s, instrumentation was improved by the availability of operational amplifiers of increasingly better quality (high open loop gain, wide frequency bandwidth. 

Calculate the slew rale and the rise time for an operational amplifier with a 50-Mf fz bandwidth in which the output changes by 10 V. 

Electronic instrumentation is available for the measurement of D.C. and A.C. voltage, current and power as well as impedance. Such instruments usually have higher sensitivities, operating frequencies and input impedance than is normally found in the electromechanical instrumentation described above. However, they may need to incorporate amplifiers and they invariably need power to operate the final display. Hence, an independent power source is needed. Both mains and battery units are available. The accuracy of measurement is very dependent on the amplifier, and bandwidth and adequate gain are important qualities. 

As a first example, let us consider a metallic thermistor inserted in fig. 3, whose resistance is, in a first approximation, expressed as R(T)=Ro(l+aT). R(T) is the resistance of a PTC thermistor at a given temperature T, Ro is the resistance at To, and I represents a suitable DC (or AC current), while A is the constant gain of a low noise amplifier, operating in a suitable bandwidth. Let us suppose that the injected current I does not induce, through the heating process, a detectable change of the resistance value. 

A family of vacuum-tube MMW sources is based on the propagation of an electron beam through a so-called slow-wave or periodic structure. Radiation propagates on the slow-wave structure at the speed of the electron beam, allowing the beam and radiation field to interact. Devices in this category are the traveling-wave tube (TWT), the backward-wave oscillator (BWO) and the extended interaction oscillator (EIO) klystron. TWTs are characterized by wide bandwidths and intermediate power output. These devices operate well at frequencies up to 100 GHz. BWOs, so called because the radiation within the vacuum tube travels in a direction opposite to that of the electron beam, have very wide bandwidths and low output powers. These sources operate at frequencies up to 1.3 THz and are extensively used in THZ spectroscopic applications [10] [11] [12]. The EIO is a high-power, narrow band tube that has an output power of 1 kW at 95 GHz and about 100 W at 230 GHz. It is available in both oscillator and amplifier, CW and pulsed versions. This source has been extensively used in MMW radar applications with some success [13]. 

At a much lower frequency, but much higher output power level, the Cornell group has recently taken advantage of the availability of kW pulse power amplifiers at 94 GHz from CPI Canada. These feature > 1 GHz instantaneous bandwidths with very flat response and can operate on a 10% duty cycle (100 W average power) with input powers less than 100 mW. In principle, this design can be scaled to higher frequencies at somewhat lower power levels. 

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