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