The balanced arrangement of {HEAD ~ sample and hold circuits} on {TAIL ~ both reference and variable oscillator sides} ensures that any switching energy transferred from the sampling system to the sample and hold capacitors will be common to both sides and therefore, rejected by the differential amplifier 
The balanced arrangement of { HEAD ~ sample and hold circuits } on { TAIL ~ both reference and variable oscillator sides } ensures that any switching energy transferred from the sampling system to the sample and hold capacitors will be common to both sides and therefore , rejected by the differential amplifier
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