Time to digital converter with error protection

Abstract

Time to digital converters (TDCs) with high resolution are disclosed. The TDC includes a first time to digital converting module, a selection and time amplifying module, a second time to digital converting module and a decoder, and is applied in estimating a time difference between a first signal and a second signal. As the delay time of the delay units of the time to digital converting modules is the unit of the time difference measurement, the first and second time to digital converting modules are responsible for the integral portion and the fractional portion of the estimated time difference, respectively. Moreover, by introducing the normalization process, the linearity of the converting characteristic of the TDC can be improved; by adding an error detection circuit to the TDC, the possible metastable problem can be prevented.

1 . A time to digital converter, comprising:
 a first time to digital converting module, for delaying a first signal to generate a plurality of delayed first signals and reading out states of the delayed first signals according to a second signal to generate first digital data;   a selection and time-amplifying module, for selecting a first specific delayed first signal from the plurality of delayed first signals, stretching the first specific delayed first signal along the time axis to generate a first reference signal, and stretching the second signal along the time axis;   a second time to digital converting module, for delaying the stretched second signal to generate a plurality of delayed and stretched second signals, and reading out states of the delayed and stretched second signals according to the first reference signal to generate second digital data; and   a decoder, for decoding at least the first and second digital data to generate an estimation of a time difference between the first and second signals.   
   
   
       2 . The time to digital converter as claimed in  claim 1 , wherein the selection and time-amplifying module further finds out a first zero bit in the first digital data, and selects the first specific delayed first signal according to the first zero bit. 
   
   
       3 . The time to digital converter as claimed in  claim 1 , wherein the selection and time-amplifying module further selects and stretches a second specific delayed first signal from the plurality of delayed first signals to generate a second reference signal, and the second specific delayed first signal lags the first specific delayed signal by a delay time. 
   
   
       4 . The time to digital converter as claimed in  claim 3 , wherein the second time to digital converting module further reads out states of the delayed and stretched second signals according to the second reference signal to generate third digital data. 
   
   
       5 . The time to digital converter as claimed in  claim 4 , wherein the decoder further decodes the third digital data and generates the estimation of the time difference between the first and second signals by performing a first calculation on the decoded first, second and third digital data. 
   
   
       6 . The time to digital converter as claimed in  claim 5 , further comprising an error detector, for detecting phases of the first reference signal and the stretched second signal and outputting an error protection enable signal to the decoder when the stretched second signal lags the first reference signal. 
   
   
       7 . The time to digital converter as claimed in  claim 6 , wherein the decoder is switched to perform a second calculation to generate the estimation when receiving the error protection enable signal. 
   
   
       8 . The time to digital converter as claimed in  claim 7 , wherein the second calculation utilizes previous decoded second digital data and previous decoded third data rather than the decoded second digital data and decoded third data to generate the estimation. 
   
   
       9 . A time to digital converter, comprising:
 a first time to digital converting module, for delaying a first signal to generate a plurality of delayed first signals, and reading out states of the delayed first signals according to a second signal to generate first digital data;   a selection and time-amplifying module, for stretching the delayed first signals and the second signal along a time axis to generate a plurality of stretched and delayed first signals and a stretched second signal, and selecting one stretched and delayed first signal from the plurality of stretched and delayed first signals as a first reference signal according to the first digital data;   a second time to digital converting module, for delaying the stretched second signal to generate a plurality of delayed and stretched second signals, and reading out states of the delayed and stretched second signals according to the first reference signal to generate second digital data; and   a decoder, for decoding at least the first and second digital data to generate an estimation of a time difference between the first and second signals.   
   
   
       10 . The time to digital converter as claimed in  claim 9 , wherein the first reference signal lags the stretched second signal and leads the other stretched and delayed first signals that lags the stretched second signal. 
   
   
       11 . The time to digital converter as claimed in  claim 9 , wherein the selection and time-amplifying module further selects another stretched and delayed first signal from the plurality of stretched and delayed first signals as a second reference signal, wherein the second reference signal lags the first reference signal and leads the other stretched and delayed first signals that lags the first reference signal. 
   
   
       12 . The time to digital converter as claimed in  claim 11 , wherein the second time to digital converting module further reads out states of the delayed and stretched second signals according to the second reference signal to generate third digital data. 
   
   
       13 . The time to digital converter as claimed in  claim 12 , wherein the decoder further decodes the third digital data, and calculates the difference between the decoded second and third digital data to normalize the decoded second digital data. 
   
   
       14 . A time to digital converter, comprising:
 a first time to digital converting module, for comparing at least a first signal and a second signal to generate first digital data representing a first portion of a difference between the first and second signals;   a time-amplifying module, for stretching a second portion of the difference between the first and second signals to generate a stretched second portion;   a second time to digital converting module, for comparing the stretched second portion with at least one stretched signal corresponding to at least one of the first signal and the second signal to generate second digital data representing the second portion of the difference between the first and second signals; and   a decoder, for decoding at least the first and second digital data to generate an estimation of a time difference between the first and second signals.   
   
   
       15 . The time to digital converter as claimed in  claim 14 , wherein the first portion corresponds to integer part of the difference, and the second portion corresponds to fractional part of the difference. 
   
   
       16 . The time to digital converter as claimed in  claim 14 , further comprising an error detector, for detecting error of the time-amplifying module and outputting an error protection enable signal to the decoder when the error is detected. 
   
   
       17 . The time to digital converter as claimed in  claim 16 , wherein the decoder decodes the first and second digital data by performing a first calculation scheme when the error protection enable signal is not received, and is switched to perform a second calculation scheme different from the first calculation scheme when receiving the error protection enable signal. 
   
   
       18 . The time to digital converter as claimed in  claim 14 , wherein the decoder further normalizes the second digital data before generating the estimation of the time difference between the first and second signals.