SerDes Sampler Circuit With Offset Correction for Faster Sampling

The sampler circuit is divided into multiple functional stages: a first stage with differential input transistors for signal reception, a second stage with cross-coupled transistors for latching, and intermediate amplification stages. This segmentation allows each stage to be optimized for its specific function, with input transistors optimized for low noise and later stages optimized for drive strength, thereby achieving high sampling speed without sacrificing drive capability.

Different regions of the circuit are designed with different transistor sizes and configurations optimized for their local functions. The input differential pair uses transistors optimized for low noise and high impedance, while the output stage uses transistors optimized for drive strength. This local optimization allows the circuit to achieve both high sampling speed and sufficient drive strength simultaneously.

The offset correction function is merged with the main signal path by using the same differential input transistors for both signal reception and offset adjustment. The gate terminals of the input transistors receive both the differential input signal and the offset voltage, eliminating the need for a separate differential input pair dedicated to offset correction. This merging reduces circuit complexity while maintaining offset correction capability.

The differential input transistors are designed to perform multiple functions: receiving the differential input signal, providing high impedance input, and accepting offset voltage adjustment. This multi-functionality eliminates the need for dedicated offset correction circuitry with separate input pairs, thereby reducing overall device complexity while maintaining precise offset correction capability.

The circuit uses dynamic control signals to manage transistor switching sequences. Clock signals and control voltages are applied dynamically to enable or disable specific transistor pairs at different times during the sampling cycle. This dynamic control allows the circuit to achieve high drive strength when needed while minimizing the effective number of transistor stacks in the critical sampling path, thereby reducing sampling time.

The sampler operates in periodic cycles with distinct phases: a sampling phase where the input signal is captured, and a hold phase where the sampled value is maintained. During the sampling phase, fewer transistor stacks are effectively in the signal path to minimize delay. During the hold phase, additional transistor stacks provide drive strength for output buffering. This periodic operation allows the circuit to achieve both high speed sampling and strong drive capability at different times in the cycle.