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If the voltage is transferred unchanged (the voltage gain A v is 1), the amplifier is a unity gain buffer; also known as a voltage follower because the output voltage follows or tracks the input voltage. Although the voltage gain of a voltage buffer amplifier may be (approximately) unity, it usually provides considerable current gain and thus ...
Date/Time Thumbnail Dimensions User Comment; current: 16:08, 31 August 2012: 720 × 720 (7 KB): Michael9422 {{subst:Upload marker added by en.wp UW}} {{Information |Description = {{en|A simple NPN transistor amplifier circuit diagram with transistor labels.}} |Source = I created a postscript file, and converted it too SVG using the pstoedit program. |Date = ...
A circuit diagram of a buffer amplifier made using an operational amplifier. = = (realistically, the differential input impedance of the op-amp itself, 1 MΩ to 1 TΩ) Date: 26 January 2009: Source: Own work
The current gain is unity, so the same current is delivered to the output load R L, producing by Ohm's law an output voltage v out = v Thév R L / R S, that is, the first form of the voltage gain above. In the second case R S << 1/g m and the Thévenin representation of the source is useful, producing the second form for the gain, typical of ...
The peaking of the gain curve is typical of uncompensated or poorly compensated transimpedance amplifiers. The curve labeled A OL is the open-loop response of the amplifier. The feedback factor, plotted as a reciprocal, is labeled 1/β. In Fig. 4 the 1/β curve and A OL form an isosceles triangle with the frequency axis.
The input signal is applied across the ground and the base circuit of the transistor. The output signal appears across ground and the collector of the transistor. Since the emitter is connected to the ground, it is common to signals, input and output. The common-emitter circuit is the most widely used of junction transistor amplifiers.
Thus this circuit finds applications as a voltage buffer. In other words, the circuit has current gain (which depends largely on the h FE of the transistor) instead of voltage gain. A small change to the input current results in much larger change in the output current supplied to the output load.
This is the only first order source of mismatch in the three-transistor Wilson current mirror [8] Second, at high currents the current gain, β, of transistors decreases and the relation of collector current to base-emitter voltage deviates from = (). The severity of these effects depends on the collector voltage.