OTA Voltage Amplifier Circuit Diagram:

A basic OTA voltage amplifier circuit diagram is shown in Fig. 41.4.

At room temperature (T = 300 K), the output current,

Now, if the whole output current I_out flows into the R_L. This will occur only if [I_B⁺ ≪ I_out], thus

Thus, the R_L also contributes to voltage gain. And to have I_B⁺ ≪ I_out, we select an op-amp voltage follower to avoid loading effects.

The controlling current I_c also alters the output, so we connect an external resistance R_ext (between pair 5 and ground, as shown in Fig. 41.5 (a) so that

One approach, as shown in Fig. 41.5 (b), to set controlling current l_c is using a control voltage V_c, so that

Another approach for setting controlling current I_c is by using a current source, as shown in Fig. 41.5 (c). (One may employ FET, BJT, an op-amp, an l_c current chip or another 3080 as current source).