# Differential circuit with constant current

Posted on Dec 11, 2010

Differential amplifier with a constant current source, as shown in Figure 1-27. Thus, as long as, c3 and kept constant, cl, n can not be simultaneously increased or reduced sim

ultaneously, thus inhibiting the voltage drift. Their differential circuit input signal, the output is divided into four different ways: double-ended input, double-ended output; double-ended input into a single-ended output; single-ended input, double-ended output; single-ended input, single-ended output. As shown in Figure 1-28. Magnification can be connected in four umbrella is: regardless of access method, as long as a single-ended output, the magnification of the basic amplification circuit half; if it is double-ended output, the magnification and the same basic amplifier circuit o differential amplifier circuit is almost always pre-stage amplifier circuit input section o Therefore, its output is always going to base this amplification circuit. This single-ended output differential circuit is not a problem, while the double-ended output differential circuit would be inconvenient o because although it has two outputs, but not between the input signal and the common terminal, the single end output, you can not play to the advantages of the differential circuit. Hence the need for a double-ended to single output terminal matching circuit, which is the mirror current source circuit shown in Figure 1-29. In Figure 1-29, VT3, VT4 constitute a mirror current source, therefore: Ic, 3 J d, and, c3 - Icl, so: Ic4 Icl output current D o Id - lc2 Icl - Ic2 0 when the common mode input (input terminal when two equal amplitude signals to common mode input), I {: 1 Ic2 so f. A, c2 0 and the same double-ended output. Differential input (two input terminal input equal in magnitude and opposite polarity signals, called differential mode input): Icl FIcl a Icl, Ic2 F, c2 + Ic2 because Icl F, spit so. F2AlC. That differential input, the output current is a single-tube double current output, and also double-ended output the same. In the example above the circuit schematic will encounter later.

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