Pedestal drift and cable pickup problems in multiplexed analog signal transmission

Sample-and-hold circuits followed by analog multiplexing are often used to reduce the number of cables required between large multielement high-energy detectors and their associated analog-to-digital converters. All sample-and-hold circuits have charge-injection pedestals that can vary with time, temperature, and power supply voltages. These variations are often correlated among many channels so that total energy sums may be degraded, even though individual pedestal drifts remain negligible. A double-sampling system is described that substantially decreases charge-injection pedestals and their variations. The effects of low-frequency pickup in long signal cables, which also tend to be correlated, are very much reduced as well.