The correcting transistor serves to maintain mirrored currents between each of the source transistors and each of {TAIL ~ the sink transistors} to eliminate {HEAD ~ the implications} of inequivalent voltage drop across corresponding series of transistors in the amplifier so that the range of output voltage swing, even in low supply voltage applications, closely approaches the value of the power supply voltage 
The correcting transistor serves to maintain mirrored currents between each of the source transistors and each of { TAIL ~ the sink transistors } to eliminate { HEAD ~ the implications } of inequivalent voltage drop across corresponding series of transistors in the amplifier so that the range of output voltage swing , even in low supply voltage applications , closely approaches the value of the power supply voltage
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