The amplifiers A2 and or A4 in FIG. 26, FIG. 27, and or FIG. 28 will provide isolation of electrical current flowing into the emitter of Q3 and or Q4. The amplifiers A2 and or A4 in FIG. 26, FIG. 27, and or FIG. 28 will provide isolation of electrical current flowing into the collector of Q5 or to a current source that includes a DC current. The amplifiers A2 and or A4 in FIG. 26, FIG. 27, and or FIG. 28 will provide isolation of electrical current flowing into the collector of Q5 or to a current source that includes DC current and or AC current. The amplifiers A2 and or A4 in FIG. 26, FIG. 27, and or FIG. 28 prevent electrical current flowing into the emitter of Q3 and or Q4 via R6, R7, R8, R9, Q6, and or Q7. The amplifiers A2 and or A4 in FIG. 26, FIG. 27, and or FIG. 28 absorb or sink electrical current from R6, R7, R8, R9, Q6, and or Q7. The amplifiers A2 and or A4 in FIG. 26, FIG. 27, and or FIG. 28 preserves an exponential or logarithmic characteristic of bipolar transistors (e.g., Q3 and or Q4) when current(s) is driven to the collectors of Q3 and Q4 via the emitters of Q1 and or Q2.
