Current Mirror Radio Circuits

 

A Collection of mostly current mirror regenerative radio circuits


A current mirror circuit is an electronic circuit that replicates a current flowing through one active device (such as a transistor) by controlling the current in another active device. This is achieved by ensuring that the two devices have the same base-emitter or gate-source voltage. As a result, the output current of the current mirror is a replica of the input current, with a high output resistance and a low input resistance.

Current mirror circuits are commonly used in analog circuits to provide bias currents and active loads. Bias currents are used to set the operating point of transistors, while active loads are used to provide a stable load impedance for amplifiers. Current mirrors can also be used to create current sources, which are circuits that provide a constant current regardless of the load.

Basic Current Mirror.


In radio circuits, the current mirror effect can be exploited at DC because inductors have low to near zero DC resistance. This means that the current flowing through an inductor at DC is essentially the same as the current flowing through the rest of the circuit. This allows the current mirror to accurately replicate the input current at DC.
An inductor in a current mirror circuit can divert RF current elsewhere, for example into the base of a transistor


Figure 1.
In figure 1, Q1 and Q2 form a current mirror with Q3 at DC. Q1 and Q2 form a differential pair oscillator. Just at the threshold of oscillation the Q of the resonant circuit is increased by loss cancellation. The RF signal at the collector of Q2 is diverted into the base of Q3 which acts as "square law" AM detector.

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Figure 2.

Figure 2 shows the same idea using a Vackar oscillator configuration.


Figure 3.



Figure 3, makes use of a FET input stage. D1 provides some negative bias to the gate to reduce current draw and could also be a red LED for lower current operation.
Figure 4.

Figure 4, is a miscellaneous collection of regenerative radio circuits.



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