Synchronizer circuit which controls switching of clocks based upon synchronicity, asynchronicity, or change in frequency
First Claim
1. A circuit for synchronizing first and second frequencies of first and second clock signals comprising:
- a synchronizer includinga first flip-flop circuit coupled to the first and second clock signals and having an output; and
a second flip-flop circuit having a first input coupled to the output of the first flip-flop, a second input coupled to the second clock signal, and an output;
a switching circuit having first and second inputs and an output, wherein the first input is coupled to the first clock signal and the second input is coupled to the output of the second flip-flop circuit; and
control circuit which determines whether the first and second frequencies are synchronous or asynchronous, which causes the switching circuit to select the first input of the switching circuit when the first and second frequencies are asynchronous, and which causes the switching circuit to select the second input of the switching circuit when the first and second frequencies are synchronous.
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Accused Products
Abstract
A synchronizer circuit which bypasses synchronous clock signals or maintains synchronicity of synchronous clock signals without degrading system performance. The synchronizer circuit includes a synchronizer having first and second clock signal inputs. A switching circuit couples to the first clock signal and to the output of the synchronizer. The synchronizer circuit is preferably programmable, and includes a control circuit which determines whether the first and second frequencies are synchronous or asynchronous, which causes the switching circuit to select the synchronizer output when the first and second frequencies are asynchronous, and which causes the switching circuit to select the first clock signal when the first and second frequencies are synchronous. The switching circuit may also couple to a first stage output of the synchronizer, and the control circuit may cause the switching circuit to select the first stage output when the first and second frequencies are synchronous and either of the first and second frequencies is a multiple of the other. The switching circuit may also include logic elements for decoupling the first and second clock signals from a multi-frequency device when the first and second frequencies are changing.
67 Citations
16 Claims
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1. A circuit for synchronizing first and second frequencies of first and second clock signals comprising:
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a synchronizer including a first flip-flop circuit coupled to the first and second clock signals and having an output; and a second flip-flop circuit having a first input coupled to the output of the first flip-flop, a second input coupled to the second clock signal, and an output; a switching circuit having first and second inputs and an output, wherein the first input is coupled to the first clock signal and the second input is coupled to the output of the second flip-flop circuit; and control circuit which determines whether the first and second frequencies are synchronous or asynchronous, which causes the switching circuit to select the first input of the switching circuit when the first and second frequencies are asynchronous, and which causes the switching circuit to select the second input of the switching circuit when the first and second frequencies are synchronous. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A circuit for synchronizing first and second frequencies of first and second clock signals comprising:
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a two-stage synchronizer including a first stage having first and second inputs coupled to the first and second clock signals and an output, and having a second stage having a first input coupled to the output of the first stage and a second input coupled to the second clock signal and an output; a switching circuit having first, second, and third inputs and an output, wherein the first input is coupled to the first clock signal and the second input is coupled to the output of the second stage and the third input is coupled to the output of the first stage; and control circuit which determines whether the first and second frequencies are synchronous or asynchronous, and which causes the switching circuit to select the second input of the switching circuit when the first and second frequencies are asynchronous, the third input of the switching circuit when the first and second frequencies are synchronous and either of the first and second frequencies is an integer multiple of the other, and the first input of the switching circuit when the first and second frequencies are synchronous and either of the first and second frequencies is not an integer multiple of the other. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16)
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Specification