Integrating analog to digital converter

Abstract

An integrating analog to digital converter (ADC) is disclosed that comprises a Delay Locked Loop (DLL) (2, 50) which is synchronized to a reference clock signal (12). A rising edge of a clock signal therefore propagates through the DLL once each clock cycle. In use, the integrating ADC converts an analog input signal to a digital output signal dependent upon a timing measurement of an integration carried out by an integrator (4). The timing measurement is taken by reading the logical states of the individual delay cells in the DLL. This enables the position of the rising edges of the clock signal to be determined and used as a timing measurement. The timing measurement is in the form of a digital thermometer code that can be converted into a binary number. By using a DLL to take a timing measurement, the effect of process and temperature variations is reduced by the closed loop feedback of the DLL. In another embodiment, a multiplying DLL (MDLL) is used. In a further embodiment a ring oscillator is used instead of a DLL. In that embodiment a calibration unit is used to compensate for the effects of process and temperature variations.

Description

technical field [0001] This invention relates to analog-to-digital converters (ADCs), and more particularly to ADCs that utilize timing of the integration of a signal to achieve analog-to-digital conversion. The invention also relates to a method of converting an analog signal into a digital signal. Background technique [0002] Many applications require the conversion of continuous analog signals to discrete digital signals. ADC design typically involves a tradeoff between resolution (the number of discrete levels contained in a digitized signal) and speed (the number of samples that can be sampled per second). [0003] Integrating ADC is known. They can achieve high resolution by timing the integration of the signal to a reference level. The time taken is proportional to the amplitude of the signal to be converted into a digital signal. Integrating ADCs require a high precision timing reference that can operate at frequencies many times higher than the sampling frequen...

AI Technical Summary

Problems solved by technology

However, process and temperature variations introduce variations in delay line operation that can affect the accuracy of the output

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