Clock pulse generator apparatus with reduced jitter clock phase
Clock pulse generator apparatus comprising a clock pulse generator for generating a train of primary clock pulses having leading and trailing edges. A delay line produces a train of delayed clock pulses presenting delayed edges whose timing relative to corresponding edges of the primary clock pulses is defined by the delay line. A logic circuit produces a train of combined clock pulses presenting leading and trailing edges defined alternately by one of the delayed edges and the corresponding edge of the primary clock pulse, so that the combined clock pulses comprise active clock phases having widths defined by the delay line; the variability of the widths of the active clock phases is smaller than the variability of the positions of the leading and trailing edges of the primary clock pulses.
1 . Apparatus for converting between analogue and digital signals comprising:
continuous-time sigma-delta conversion means; and
clock pulse generator apparatus comprising a clock pulse generator for generating a train of return-to zero primary clock pulses each having leading and trailing edges defining alternately an active clock phase and a non-active clock phase;
delay means for producing a train of delayed clock pulses presenting delayed edges whose timing relative to corresponding edges of said primary clock pulses is defined by said delay means, and
combining means for producing a train of combined clock pulses presenting leading and trailing edges defined alternately by one of said delayed edges and the corresponding edge of the primary clock pulse, so that the active clock phases of said combined clock pulses have widths defined by said delay means, the variability of said widths of said active clock phases being smaller than the variability of the positions of said leading and trailing edges of said primary clock pulses, and the widths of said non-active clock phases varying as a function of variation in the positions of said primary clock pulses.
2 . Apparatus for converting between analogue and digital signals as claimed in claim 1 wherein said delay means comprises a series of cascaded, substantially identical delay elements.
3 . Apparatus for converting between analogue and digital signals as claimed in claim 2 wherein said delay means comprises a further series of cascaded delay elements substantially identical to the first said delay elements, adjustment means responsive to the delay of said further series relative to a pulse period of said train of primary clock pulses for applying an adjustment signal to tend to correct the delay of said further series of delay elements relative to a pulse period, said adjustment signal being averaged over a plurality of clock periods, and means for applying said adjustment signal to adjust the delay of the delay elements of said first series.
4 . Apparatus for converting between analogue and digital signals as claimed in claim 2 wherein each of said delay elements comprises a respective capacitive element, current supply means responsive to an signal input to the delay element for supplying a controlled current to said respective capacitive element, and trigger means responsive to the voltage at said respective capacitive element.
5 . Apparatus for converting between analogue and digital signals as claimed in claim 1 , wherein said continuous-time sigma-delta conversion means comprises integration means for integrating a signal over periods of time defined by said widths of said active clock phases.
6 . Apparatus for converting between analogue and digital signals as claimed in claim 5 , wherein said continuous-time sigma-delta conversion means comprises digital-to-analogue converter means whose operation is responsive to said train of combined clock pulses.
7 . Apparatus for converting an analogue signal to a digital signal as claimed in claim 6 , wherein said continuous-time sigma-delta conversion means comprises an input for receiving said analogue signal, an output for said digital signal and a feedback loop from said output including said digital-to-analogue converter means.
8 . Apparatus for converting a digital signal to an analogue signal as claimed in claim 6 , wherein said continuous-time sigma-delta conversion means comprises an input for receiving said digital signal and an output for said analogue signal, said digital-to-analogue converter means being in series between said input and said output.