FIG. 23 shows a differential amplifier with diodes, D1 and D2, as local feedback elements. These diodes, D1 and or D2 lower the output noise at either or both collectors of Q1 and or Q2.
In FIG. 23, the diodes, D1 and or D2, may also reduce distortion of the amplifier at the collectors of Q1 and or Q2 when the amplifier is configured as a differential amplifier with an input signal Vin shown coupled to the base of Q1 or alternatively a signal may be coupled to the base of Q2. The diodes, D1 and or D2, may also reduce distortion of the amplifier at the collectors of Q1 and or Q2 when the amplifier is configured as a voltage controlled amplifier with a control signal Vin shown coupled to the base of Q1 or alternatively a signal may be coupled to the base of Q2, wherein in an input signal (e.g., AC signal) is provided by Vopt. By controlling Vin, the signal at the collector of Q1 and or Q2 (e.g., via resistors R4 and or R5) provides an amplitude controlled signal of Vopt. For example, if Vin includes a DC signal, the gain or amplitude of Vopt is controlled or varied via Vin. In another example, if Vin is a modulating signal, then an amplitude modulated Vopt is provided at the collector of Q1 and or at the collector of Q2. The diodes D1 and or D2 provides for the voltage controlled amplifier (e.g., Q1, Q2, and or Q5) lower distortion and or noise at outputs provided by the collector(s) of Q1 and or Q2.
