Clock frequency overshoot detection circuit
View Patent ↗An electronic circuit operating on a first clock signal includes a clock frequency overshoot detection circuit for detecting frequency overshoots in the first clock signal. The clock frequency overshoot detection circuit includes a shift register having an even number plurality of flip-flops. The flip-flops toggle to generate output bit patterns indicative of a frequency overshoot condition. A comparator connected to the shift register generates a comparison signal on detecting the frequency overshoot condition. A latch circuit connected to the comparator generates a frequency overshoot indication signal and the electronic circuit is shifted to a second (or safe) clock signal until the frequency of the first clock signal is rectified.
1. A clock frequency overshoot detection circuit, comprising:
a clock gating cell for receiving a first clock signal and generating a gated clock signal based on a count signal;
a shift register connected to the clock gating cell and including at least two pairs of flip-flops, wherein each pair of flip-flops includes a set flip-flop and a reset flip-flop, and wherein an input terminal of each flip-flop is connected to an output terminal of a previous flip-flop and an output terminal of a last flip-flop is connected to an input terminal of a first flip-flop, and wherein the gated clock signal is provided to respective clock inputs of each of the flip-flops such that an output of each of the flip-flops toggles at each pulse of the gated clock signal, thereby generating an output bit pattern;
a comparator, connected to the output terminals of each of the flip-flops, for generating a comparison signal;
a latch circuit, connected to the comparator, and having a clock input for receiving the comparison signal and a data input terminal for receiving a predefined logic value, wherein the latch circuit outputs a frequency overshoot indication signal; and
a binary counter, connected to the clock gating cell, for generating and providing the count signal to the clock gating cell.
2. The clock frequency overshoot detection circuit of claim 1 , wherein the first clock signal is generated by a phase-locked loop (PLL) circuit.
3. The clock frequency overshoot detection circuit of claim 1 , wherein the clock frequency overshoot detection circuit is integrated in an electronic circuit that functions using the first clock signal.
4. The clock frequency overshoot detection circuit of claim 3 , further comprising a resistive-capacitive (RC) oscillator circuit that generates a second clock signal.
5. The clock frequency overshoot detection circuit of claim 4 , further comprising a synchronizer circuit having a first input terminal connected to the latch circuit and receiving the frequency overshoot indication signal and a second input terminal connected to the RC oscillator circuit and receiving the second clock signal, wherein the synchronizer circuit synchronizes the operation of the electronic circuit to the second clock signal based on the frequency overshoot indication signal.
6. The clock frequency overshoot detection circuit of claim 5 , further comprising a reset circuit, connected between the synchronizer circuit and the binary counter, for providing a RESET signal to the binary counter.
7. The clock frequency overshoot detection circuit of claim 1 , wherein each of the flip-flops is a D flip-flop.
8. The clock frequency overshoot detection circuit of claim 1 , wherein the comparator circuit is formed with digital logic circuits.
9. An electronic circuit that receives a first clock signal from a clock generation circuit, comprising;
a clock frequency overshoot detection circuit for detecting a frequency overshoot in the first clock signal, wherein the clock frequency overshoot detection circuit includes,
a clock gating cell for receiving the first clock signal and generating a gated clock signal based on a count signal;
a shift register connected to the clock gating cell and including at least two pairs of flip-flops, wherein each pair of flip-flops includes a set flip-flop and a reset flip-flop, and wherein an input terminal of each flip-flop is connected to an output terminal of a previous flip-flop and an output terminal of a last flip-flop is connected to an input terminal of a first flip-flop, and wherein the gated clock signal is provided to respective clock inputs of each of the flip-flops such that an output of each of the flip-flops toggles at each pulse of the gated clock signal, thereby generating an output bit pattern;
a comparator, connected to the output terminals of each of the flip-flops, for generating a comparison signal;
a latch circuit, connected to the comparator and having a clock input for receiving the comparison signal and a data input terminal for receiving a predefined logic value, wherein the latch circuit outputs a frequency overshoot indication signal; and
a binary counter, connected to the clock gating cell, for generating and providing the count signal to the clock gating cell.
10. The electronic circuit of claim 9 , wherein the electronic circuit further receives a second clock signal generated by a resistive-capacitive (RC) oscillator circuit.
11. The electronic circuit of claim 10 , further comprising a synchronizer circuit having a first input terminal connected to the latch circuit and receiving the frequency overshoot indication signal and a second input terminal connected to the RC oscillator circuit and receiving a second clock signal, wherein the synchronizer circuit synchronizes the operation of the electronic circuit to the second clock signal based on the frequency overshoot indication signal.
12. The electronic circuit of claim 11 , further comprising a reset circuit connected between the synchronizer circuit and the binary counter, for providing a RESET signal to the binary counter.
13. The electronic circuit of claim 9 , wherein each of the flip-flops is a D flip-flop.
14. The electronic circuit of claim 9 , wherein the comparator circuit is formed with digital logic circuits.
15. A clock frequency overshoot detection circuit, comprising:
a clock gating cell for receiving a first clock signal and generating a gated clock signal based on a count signal;
a 32-bit shift register connected to the clock gating cell and including sixteen pairs of flip-flops, wherein each of the sixteen pairs of flip-flops includes a set flip-flop and a reset flip-flop, and wherein an input terminal of each flip-flop is connected to an output terminal of a previous flip-flop and an output terminal of a last flip-flop is connected to an input terminal of a first flip-flop, and wherein the gated clock signal is provided to respective clock inputs of each of the flip-flops such that an output of each of the flip-flops toggles at each pulse of the gated clock signal, thereby generating an output 32-bit pattern;
a comparator, connected to the output terminals of each of the flip-flops, for generating a comparison signal;
a latch circuit, connected to the comparator and having a clock input for receiving the comparison signal and a data input terminal for receiving a predefined logic value, wherein the latch circuit outputs a frequency overshoot indication signal; and
a binary counter, connected to the clock gating cell, for generating and providing the count signal to the clock gating cell.
16. The clock frequency overshoot detection circuit of claim 15 , wherein the first clock signal is generated by a phase-locked loop (PLL) circuit.
17. The clock frequency overshoot detection circuit of claim 15 , wherein the electronic circuit further receives a second clock signal generated by a resistive-capacitive (RC) oscillator circuit.
18. The clock frequency overshoot detection circuit of claim 17 , further comprising a synchronizer circuit having a first input terminal connected to the latch circuit and receiving the frequency overshoot indication signal and a second input terminal connected to the RC oscillator circuit and receiving a second clock signal, wherein the synchronizer circuit synchronizes the operation of the electronic circuit to the second clock signal based on the frequency overshoot indication signal.
19. The clock frequency overshoot detection circuit of claim 18 , further comprising a reset circuit connected between the synchronizer circuit and the binary counter, for providing a RESET signal to the binary counter.
20. The clock frequency overshoot detection circuit of claim 15 , wherein each of the flip-flops is a D flip-flop.