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图1的电路能提供相当高的输入阻抗,而且电路增益可由外部控制。电路有两种工作方式供使用者选择,一种为固定增益;另一种为1到1000之间的可调增益。电路使用的放大器相当普通,只要一个增益电阻,电路的基本增益为(1+R_f/R_g)。 R_g为无穷大时,增益为1,增益的选择是采用类比开关与电阻。因为类比开关本身就有不小的内阻,因此保持R_2对内阻于高比值是相当重要的工作,否则会造成非线性增益变化的结果。
The circuit of Figure 1 provides a fairly high input impedance and the circuit gain can be externally controlled. There are two ways for the user to choose the circuit, one for the fixed gain; the other for the adjustable gain of 1 to 1000. The amplifier used in the circuit is quite common, as long as a gain resistor, the basic gain of the circuit is (1 + R_f / R_g). When R_g is infinite, the gain is 1, the choice of gain is analog switch and resistor. Since the analog switch itself has a small internal resistance, it is important to keep R 2 at a high internal resistance, otherwise it will result in a nonlinear gain change.