RF phase shifters are twin-ported devices that alter the phase of an output signal in response to an external signal. Variable phase shifters change the output signal phase by applying a variable control signal. There are two basic types of variable phase shifters: analog and digital. Analog phase shifters change the output phase with a continuous signal, usually voltage. In turn, the control voltage determines the voltage range used to change the phase of the output signal. Digital phase shifters use a digital signal as the control element. The number of bits in this signal determines the number of steps in each phase change. If n equals the number of bits in the digital control signal, then the number of output states (phase changes) is 2n .
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