Digital Variable Gain Amplifier
Another version of the VGAs are the digital controlled. It is possible to change the gain using a digital signal.
The digitally controlled amplifier uses a "stepped" approach giving the circuit graduated increments of gain selection. This can be done in several fashions, but certain elements remain in any design.
At its most basic form, a toggle switch strapped across the feedback resistor can provide a Hi-LO gain setting. While this is not a computer controlled function, it describes the core function. With eights switches and eight resistors in the feedback loop, each switch can enable a particular resistor to control the feedback of the amplifier. If each switch was converted to a relay, a microcontroller could be used to activate the relays to attain the desired amount of gain.
Relays can be replaced with Field Effect Transistors of an appropriate type to reduce the mechanical nature of the design. Other devices such as the CD4053 bi-directional CMOS integrated circuit can serve well as the switching function.
To minimize the quantity of switches and resistors, combinations of resistance values can be utilized by activating multiple switches.
Read more about this topic: Variable-gain Amplifier
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