Pipelined ADC Buffering for High-Speed Flash Conversion Timing
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Solution Overview
Problem
Pipelined analog-to-digital converters face challenges at high clock speeds due to insufficient time for flash conversion, digital-to-analog conversion, and amplification, leading to impractical operation at radio frequency speeds like 3 GSPS, where comparators require more time than available.
Innovation Solution
Incorporating a buffer to operationally delay the sampled input voltage, providing additional time for flash conversion, and using a second sample-and-hold stage to manage the signal flow, while also reducing power consumption and noise introduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pipelined ADC operates at high clock speeds, then productivity increases, but conversion time becomes insufficient leading to impractical operation
Solution Approach 1:
The conversion process is divided into multiple independent stages (first flash converter, first DAC, second flash converter) that can operate in parallel or pipeline fashion. Each stage handles a portion of the conversion task, allowing the overall system to achieve high sample speeds while each individual stage has sufficient time to complete its operation.
Solution Approach 2:
The first flash converter performs preliminary conversion of the input signal to generate intermediate digital results before the second flash converter completes the final conversion. This preliminary action allows the system to start processing the next sample while previous samples are being fully converted, effectively overlapping operations to increase productivity.
2Measurement precision
If additional conversion stages are added to increase conversion time, then measurement precision improves, but device complexity increases
Solution Approach 1:
The high-precision conversion task is segmented into multiple flash converter stages, each contributing to the final precision. The first flash converter handles the most significant bits while the second handles less significant bits, achieving high overall precision through coordinated operation of simpler individual stages rather than one complex stage.
Solution Approach 2:
The system dynamically manages signal flow between stages using timing control and buffering mechanisms. The first SH output is routed to both the first flash converter and buffer, with the buffer output feeding the second flash converter. This dynamic routing allows precise control of when each stage operates, maintaining high precision while managing complexity through systematic timing management.
3Loss of time
If buffer and additional SH stage are incorporated to manage signal flow, then conversion process time increases, but power consumption increases
Solution Approach 1:
The buffer performs preliminary signal preparation by holding the first SH output voltage while the conversion processes occur. This preliminary action of voltage holding allows the second flash converter to operate with stable input without requiring continuous high-power driving, thereby extending conversion time slightly while minimizing additional power consumption through low-power buffering operation.
Data Source
AI summary
An analog-to-digital converter including a first stage and a second stage. The first stage includes a first sample-and-hold (SH) having an input coupled to a voltage input node of the ADC, and having a first SH output. The first stage also includes a buffer, a first flash converter and a first digital-to-analog converter (DAC). The buffer has an input coupled to the first SH output and has a buffer output. The first flash converter has an input coupled to the first SH output, and has a first flash converter output. The first DAC has an input coupled to the first flash converter output. The second stage includes a second flash converter having an input coupled to the buffer output.