Linear Regulator

Versal ACAP GTM Transceivers Architecture Manual (AM017)

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1.0 English

A linear regulator is usually the simplest means to provide voltage regulation for the GTM transceiver analog supply rails. Inherently, a linear regulator does not inject significant noise into the regulated output voltage. In fact, some, not all, linear regulators provide noise rejection at the output from noise present on the voltage input. Another advantage of the linear regulator is that it usually requires a minimal number of external components to realize a circuit on the printed circuit board.

There are potentially two major disadvantages to linear regulators, minimum dropout voltage, and limited efficiency. Linear regulators require an input voltage that is higher than the output voltage. This minimum dropout voltage often is dependent on the load current. Even low dropout linear regulators require a minimum difference between the input voltage and the output voltage of the regulator. The system power supply design must consider the minimum dropout voltage requirements of the linear regulators.

The efficiency of a linear regulator is dependent on the voltage difference between the input and output of the linear regulator. For instance, if the input voltage of the regulator is 2.5 VDC and the output voltage of the regulator is 1.2 VDC, the voltage difference is 1.3 VDC. Assuming that the current into the regulator is essentially equal to the current out of the regulator, the maximum efficiency of the regulator is 48%. This means that for every watt delivered to the load, the system must consume an additional watt for regulation. This power consumed by the regulator generates heat that must be dissipated by the system. Providing a means to dissipate the heat generated by the linear regulator can drive up the system cost. So even though from a simple component count and complexity cost, the linear regulator appears to have an advantage over the switching regulator, if the overall system cost is considered, including power consumption and heat dissipation, in high current applications, the linear regulator can actually be at a disadvantage.