Phase frequency to digital converter
A circuit arrangement is described comprising a first receiver configured to receive a first input signal, a second receiver configured to receive a second input signal, a first signal generator configured to generate a first pulse signal, a second signal generator configured to generate a second pulse signal, wherein a delay between a rising edge of the first pulse signal and a rising edge of the second pulse signal is proportional to a difference between the first input signal and the second input signal, a first converter configured to convert the first pulse signal to a first digital number proportional to a width of the first pulse signal, a second converter configured to convert the second pulse signal to a second digital number proportional to a width of the second pulse signal, wherein at least one of the first converter and the second converter comprises a cascade of at least two converter stages, wherein each converter stage of the at least two converter stages is configured to propagate and shrink the respective pulse signal. Also a corresponding method is described.
1. A circuit arrangement comprising:
a first receiver configured to receive a first input signal,
a second receiver configured to receive a second input signal,
a first signal generator configured to generate a first pulse signal,
a second signal generator configured to generate a second pulse signal, wherein a delay between a rising edge of the first pulse signal and a rising edge of the second pulse signal is proportional to one of a phase difference and a frequency difference between the first input signal and the second input signal,
a first converter configured to convert the first pulse signal to a first digital number proportional to a width of the first pulse signal, and
a second converter configured to convert the second pulse signal to a second digital number proportional to a width of the second pulse signal,
wherein at least one of the first converter and the second converter comprises a cascade of at least two converter stages, wherein each converter stage of the at least two converter stages is configured to propagate and shrink the respective pulse signal.
2. Circuit arrangement according to claim 1 , wherein each converter stage of the at least two converter stages comprises:
a delay circuit configured to propagate an input pulse signal after a propagation delay,
a detector configured to detected a propagated pulse signal, and
a generator configured to generate a pulse detection signal when the propagated pulse signal is detected, which pulse detection signal is indicative of the respective digital number.
3. Circuit arrangement according to claim 2 , wherein the delay circuit is
configured to propagate an input pulse signal with a falling edge after a first propagation delay, and
configured to propagate an input pulse signal with a rising edge after a second propagation delay, wherein the first propagation delay is shorter than the second propagation delay.
4. Circuit arrangement according to claim 3 , wherein the delay circuit comprises:
a first at least one transistor configured to be switched for propagating the input pulse signal with a falling edge,
a second at least one transistor of the same type as the first at least one transistor configured to be switched for propagating the input pulse signal with a rising edge,
wherein an aspect ratio of the first at least one transistor is greater than an aspect ratio of the second at least one transistor.
5. Circuit arrangement according to claim 3 , wherein the delay circuit comprises:
a first number of transistors configured to be successively switched and configured for generating at least one feed-forward signal for propagating the input pulse signal with a falling edge,
a second number of transistors configured to be successively switched and configured for propagating the input pulse signal with a rising edge.
6. Circuit arrangement according to claim 2 , wherein the delay circuit is configured to receive a propagated signal and configured to receive at least one feed forward signal.
7. Circuit arrangement according to claim 2 , wherein the detector comprises a latch and wherein the detector is configured to reset the latch and configured to switch the latch to a state indicative of a detected pulse when the propagated pulse signal is detected.
8. Circuit arrangement according to claim 7 wherein the detector is configured to keep a state of the latch when the propagated pulse signal is not detected after resetting the latch.
9. Circuit arrangement according to claim 1 , further comprising:
a resetting circuit configured to reset the first pulse signal and configured to reset the second pulse signal after a delay after the first generator has generated the first pulse signal and the second generator has generated the second pulse signal,
wherein the first generator is configured to generate the first pulse signal when the first receiver receives a rising edge of the first input signal, and
wherein the second generator is configured to generate the second pulse signal when the second receiver receives a rising edge of the second input signal.
10. Circuit arrangement according to claim 1 , further comprising an adder configured to subtract the second digital number from the first digital number to generate a third digital number.
11. Circuit arrangement according to claim 10 comprising a digitally controlled oscillator configured to receive the third digital number from the adder.
12. Circuit arrangement according to claim 1 , further comprising a frequency divider configured to divide a frequency of a clock signal, wherein an output line of the frequency divider is connected to the first receiver.
13. Circuit arrangement according to claim 1 implemented by at least one complementary metal-oxide-semiconductor circuit.
14. A method comprising:
receiving a first input signal,
receiving a second input signal,
generating a first pulse signal,
generating a second pulse signal, wherein a delay between a rising edge of the first pulse signal and a rising edge of the second pulse signal is proportional to one of a phase difference and a frequency difference between the first input signal and the second input signal,
converting the first pulse signal to a first digital number proportional to a width of the first pulse signal, and
converting the second pulse signal to a second digital number proportional to a width of the second pulse signal, wherein converting at least one of the first pulse signal and the second pulse signal to a respective digital number comprises successively propagating and shrinking the respective pulse signal.