Enabling clock signals with a phase locked loop (PLL) lock detect circuit
First Claim
1. A method of operating a clock signal generator comprising the step of:
- generating a lock signal in response to (i) a window signal and (ii) one or more control signals; and
generating an output clock signal in response to (i) an input clock signal and (ii) said lock signal, wherein said lock signal corresponds to a lock state of a phase locked loop (PLL).
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Accused Products
Abstract
A circuit for enabling and disabling generation of an output clock signal is disclosed. The circuit includes a PLL lock detect circuit that generates an active lock control signal when an output reference signal of a phase lock loop (PLL) circuit is phase locked relative to an input reference signal to the PLL. The output reference signal of the PLL, and the lock signal from the lock detect circuit, are both provided to a clock enable circuit. The clock enable circuit includes a negative edge-triggered D-type flip-flop and a two-input AND gate. The lock signal is applied to the D-input of the flip-flop, while the clock signal is applied to the clock input of the flip-flop. The lock signal is generated asynchronously relative to the input clock signal. Therefore, the flip-flop samples the lock signal on each falling edge of the clock signal so as to synchronize the lock signal relative to the input clock signal. The sampled lock signal, and the input clock signal (formed from the PLL output reference signal) are provided on respective input terminals of the AND gate. The output of the AND gate defines the output clock signal.
119 Citations
22 Claims
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1. A method of operating a clock signal generator comprising the step of:
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generating a lock signal in response to (i) a window signal and (ii) one or more control signals; and generating an output clock signal in response to (i) an input clock signal and (ii) said lock signal, wherein said lock signal corresponds to a lock state of a phase locked loop (PLL). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A clock circuit comprising:
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means for generating a lock signal in response to (i) a window signal and (ii) one or more control signals, said lock signal corresponding to a lock state of a phase locked loop (PLL) when an output reference signal of said PLL is phase locked relative to an input reference signal of said PLL; and
,means responsive to an input clock signal for generating an output clock signal according to a control signal corresponding to said lock signal. - View Dependent Claims (12, 13, 14, 15, 16)
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17. A clock circuit comprising:
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a lock detector having an output terminal for generating a lock signal in response to (i) a window signal and (ii) one or more control signals, said lock signal corresponding to a lock state of a phase locked loop (PLL) when an output reference signal of said PLL is phase locked relative to an input reference signal of said PLL; and
,a logic gate having a first input terminal for receiving an input clock signal and a second input terminal for receiving a control signal corresponding to said lock signal, said logic gate having an output terminal for generating an output clock signal in a valid state when said control signal is in an active state indicative of a lock state where said PLL is locked, said logic gate blanking said output clock signal when said control signal is in an inactive state indicative of a lock state where said PLL is unlocked. - View Dependent Claims (18, 19, 20, 21, 22)
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Specification