Analog-to-digital converter timing circuits
An analog-to-digital converter timing circuit disclosed herein uses a clock generation circuit that makes the analog-to-digital converter insensitive to input clock duty cycle. Minimum clock jitter is added to the clock signal while propagating through the disclosed circuit. A method and system are also disclosed to clock an interleaved pipelined ADC such that the operation is insensitive to input clock duty cycle and such that the clock jitter on the sampling clock edges is minimized.
1. A clock generation circuit comprising:
a clock input, two output terminals, two flip-flops, four logic NOR gates, two logic AND gates, and an inverter;
the first flip-flop is connected with its inverting output back to the input of both the first and the second flip-flop;
a non-inverting output of the first flip-flop being connected to the first input of the first NOR gate and the clock input being connected to the second input of the NOR gate;
an output of the first NOR gate being connected to the first input of the second NOR gate;
an inverting output of the second flip flop being connected to the first input of the first AND gate;
a clock input being connected to the second input of the first AND gate;
an output of the AND gate being connected to the second input of the second NOR gate;
a non-inverting output of the second flip-flop being connected to the first input of the second AND gate and a clock input being connected to the second input of the second AND gate;
an output of the second AND gate being connected to the second input of the fourth NOR gate;
an inverting output of the first flip-flop being connected to the first input of the third NOR gate;
the clock input being connected to the second input of the third NOR gate;
an output of the third NOR gate being connected to the first input of the fourth NOR gate;
a clock input being connected to the clock input of the first flip-flop and to the input of the inverter;
an output of the inverter being connected to the clock input of the second flip-flop; and
an output of the second NOR gate being connected to the first output terminal and the output of the fourth NOR gate being connected to the second output terminal.
2. A subranging ADC comprising a clock generation circuit according to claim 1 .
3. A cyclic ADC comprising a clock generation circuit according to claim 1 .
4. A pipelined ADC circuitry comprising a clock generation circuit according to claim 1 .
5. A clock generation circuit used to clock ADC circuitry, the clock generation circuit comprising:
an input clock;
a plurality of output clocks;
an enabling circuitry to divide a clock rate by two and to generate enable signals toggling on positive clock edges of the input clock and enable signals toggling on negative clock edges of the input clock; and
a plurality of digital gates to generate the output clocks based on enable signals received from the enabling circuitry and timed only by one edge of the input clock.
6. The clock generation circuit of claim 5 , wherein the ADC circuitry comprises double sampling ADCs.
7. The clock generation circuit of claim 5 , wherein the ADC circuitry comprises a subranging ADC.
8. The clock generation circuit of claim 5 , wherein the ADC circuitry comprises a cyclic ADC.
9. The clock generation circuit of claim 5 , wherein the ADC circuitry comprises a pipelined ADC.
10. The clock generation circuit of claim 5 , wherein the enabling circuitry includes first and second flip-flops and an inverter, and wherein the plurality of digital gates comprises first, second, third, and fourth logic NOR gates and first and second logic AND gates, wherein:
the first flip-flop is connected with its inverting output back to an input of both the first flip-flop and the second flip-flop;
a non-inverting output of the first flip-flop is connected to a first input of the first NOR gate, and the clock input is connected to a second input of the first NOR gate;
an output of the first NOR gate is connected to a first input of the second NOR gate;
an inverting output of the second flip flop is connected to a first input of the first AND gate;
a clock input is connected to a second input of the first AND gate;
an output of the first AND gate is connected to a second input of the second NOR gate;
a non-inverting output of the second flip-flop is connected to a first input of the second AND gate, and a clock input is connected to a second input of the second AND gate;
an output of the second AND gate is connected to a second input of the fourth NOR gate;
an inverting output of the first flip-flop is connected to a first input of the third NOR gate;
the clock input is connected to a second input of the third NOR gate;
an output of the third NOR gate is connected to a first input of the fourth NOR gate;
a clock input is connected to the clock input of the first flip-flop and to the input of the inverter;
an output of the inverter is connected to the clock input of the second flip-flop; and
an output of the second NOR gate is connected to a first output terminal and the output of the fourth NOR gate is connected to a second output terminal.
11. A pipelined analog-to-digital converter (ADC) including a plurality of serially connected analog-to-digital pipeline stages, each of the stages comprising:
a stage input to which an input analog signal to be converted is applied;
two parallel ADC channels, each channel comprising a sub-ADC for quantizing the input analog signal received at the stage input into a digital signal of a given number of bits, a digital-to-analog converter (DAC) for converting the digital signal to an analog signal, a sampling network for sampling the input analog signal received at the stage input, a subtraction circuit for subtracting the analog signal produced by the DAC from the input analog signal from the sampling network to produce a residual signal, and an input stage operational transconductance amplifier (OTA) for amplifying the residual signal; and
an OTA output stage for receiving and amplifying the residual signal from the input stage OTA for both of the channels; and
a stage output for outputting the residual signal amplified by the OTA output stage, said stage output being coupled to a stage input of a subsequent pipeline stage, if any;
wherein the two parallel ADC channels of each stage work in antiphase such that when one channel is in a hold phase, the other channel is in a track phase, and wherein the channels alternate between hold and track phases, and the OTA output stage switches operation from one channel to another.
12. The pipelined ADC of claim 11 , further comprising circuitry for switching bias current in an OTA input stage on and off when the ADC channel containing the OTA input stage is switched between hold and track phases, respectively.
13. The pipelined ADC of claim 11 , further comprising a clock generation circuit for generating timing pulses for track and hold phase switching.
14. The pipelined ADC of claim 13 , wherein the clock generation circuit comprises:
an input clock;
a plurality of output clocks;
an enabling circuitry to divide a clock rate by two and to generate enable signals toggling on positive clock edges of the input clock and enable signals toggling on negative clock edges of the input clock; and
a plurality of digital gates to generate the output clocks based on enable signals received from the enabling circuitry and timed only by one edge of the input clock.