Provided is an AD converter that converts an input analog signal into a digital signal, comprising an integrator that sequentially integrates signal levels of the analog signal to obtain an integrated waveform, and outputs the integrated waveform; a digital converting section that detects, with prescribed units of temporal resolution, a transition timing, which is a timing at which a magnitude relationship between a signal level of the integrated waveform and a prescribed reference value transitions to a predetermined state; a feedback section that controls the signal level of the integrated waveform with a control period longer than a unit of temporal resolution, according to a result of the detection by the digital converting section; and a signal processing section that generates the digital signal based on the detection result by the digital converting section.
1. An AD converter that converts an input analog signal into a digital signal, comprising:
an integrator that sequentially integrates signal levels of the analog signal to obtain an integrated waveform, and outputs the integrated waveform;
a digital converting section that detects, with prescribed units of temporal resolution, a transition timing, which is a timing at which a magnitude relationship between a signal level of the integrated waveform and a prescribed reference value transitions to a predetermined state;
a feedback section that controls the signal level of the integrated waveform with a control period longer than a unit of temporal resolution, according to a result of the detection by the digital converting section; and
a signal processing section that generates the digital signal based on the detection result by the digital converting section.
2. The AD converter according to claim 1 , wherein
the feedback section controls the signal level of the integrated waveform with the control period, which is n units of temporal resolution, where n is an integer greater than 1.
3. The AD converter according to claim 2 , wherein
the feedback section adds or subtracts a signal level corresponding to the reference value to or from the signal level of the integrated waveform at a control timing corresponding to the transition timing detected by the digital converting section in the control period.
4. The AD converter according to claim 3 , wherein
the feedback section detects the control timing in the control period with units of temporal resolution that are substantially equal to the units of temporal resolution of the digital converting section.
5. The AD converter according to claim 4 , wherein
the digital converting section sequentially detects whether the magnitude relationship between the signal level of the integrated waveform and the prescribed reference value has transitioned to a prescribed state, at sampling timings with periods shorter than the control period, and
the feedback section controls the signal level of the integrated waveform after a plurality of sampling timings have passed since a sampling timing at which the digital converting section detects the transition timing.
6. The AD converter according to claim 5 , wherein
the feedback section controls the signal level of the integrated waveform according to a duration over which the magnitude relationship continues to be in the prescribed state.
7. The AD converter according to claim 5 , wherein the digital converting section includes:
a plurality of delay elements connected in cascade that generate a plurality of strobe signals by sequentially delaying a reference clock having a period that is the same as the control period; and
a detection circuit that, in each cycle of the reference clock, detects the magnitude relationship between the signal level of the integrated waveform and the reference value at sampling timings according to the strobe signals output by the delay elements.
8. The AD converter according to claim 7 , wherein
when the detection circuit detects the transition timing in a cycle of the reference clock, the feedback section adds or subtracts a predetermined signal level to or from the signal level of the integrated waveform in a cycle that is after the cycle of the reference clock in which the transition timing is detected.
9. The AD converter according to claim 8 , wherein
upon detecting the transition timing in a cycle of the reference clock, the detection circuit generates timing information that indicates a timing, in the cycle, of the strobe signal that detected the transition timing, and
the feedback section includes:
a timing generating section that generates a feedback signal by delaying, according to the timing information, a pulse of the reference clock in a cycle following the cycle in which the transition timing is detected; and
a level calculating section that adds or subtracts a predetermined signal level to or from the signal level of the integrated waveform according to the feedback signal.
10. The AD converter according to claim 7 , further comprising a setting section that sets a delay time for each of the delay elements.
11. The AD converter according to claim 7 , further comprising a level comparing section that outputs a logic value according to a comparison result between the signal level of the integrated waveform and the reference value, wherein
the detection circuit detects the logic value output by the level comparing section, at each of the sampling timings.
12. The AD converter according to claim 2 , wherein
the feedback section adds or subtracts a signal level corresponding to the transition timing detected by the digital converting section to or from the signal level of the integrated waveform.
13. The AD converter according to claim 12 , wherein
the feedback section controls the signal level of the integrated waveform at a set control timing in the control period.
14. The AD converter according to claim 1 , wherein
the digital converting section sequentially detects whether the magnitude relationship between the signal level of the integrated waveform and the prescribed reference value has transitioned to a prescribed state, at sampling timings having periods less than the control period.
15. The AD converter according to claim 1 , wherein
the integrator sequentially integrates a signal level of a first analog signal to obtain an integrated waveform, and outputs the resulting integrated waveform, and
the digital converting section acquires, as the prescribed reference value, a signal level of a waveform obtained by sequentially integrating a signal level of a second analog signal.