11.2. Broad-band current amplifiers

Fig. 11.2. Broad-band current amplifiers, (a) By replacing the feedback resistor in Fig. 11.1 with a resistor network, the cutoff frequency of the amplifier can be greatly increased, but the Johnson noise is increased, (b) Broad-band current amplifier with a compensation capacitor. By introducing a condensation capacitor C2, the effect of Q can be reduced. Under the condition CiRi = C2R2, the frequency range is substantially expended. The Johnson noise is not affected.

It should be noted that all the elements in the circuits of Fig. 11.2, including the circuit hoard, in ultra-high-vacuum (UHV) compatible form, are available commercially. Therefore, the entire broad-band current amplifier can be enclosed in a UHV ehamber and located as close as possible to the tip. 

Figure 9.6. Differential amplifier performance with common-mode interference signals, (a) Upper trace 10-kHz sine wave with superimposed common-mode noise as amplified by conventional amplifier lower trace same signal amplified by differential amplifier, (b) Upper trace 10-kHz square wave with superimposed 60-Hz hum and broad-band noise as amplified by single-ended amplifier middle trace same signal as amplified by differential amplifier lower trace residual noise removed by filtering, (c) Circuit schematic for transistor differential amplifier with constant-current emitter stage, (d) Vacuum-tube differential amplifier in long-tailed pair configuration. (See Ferris, 1963.)...

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