Clock-synchronous type semiconductor memory device capable of outputting read clock signal at correct timing
First Claim
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1. A synchronous type semiconductor memory device, comprising:
- a phase synchronization circuit for generating an internal clock signal synchronized in phase with an externally supplied external clock signal, said phase synchronization circuit including a voltage controlled oscillator having a feedback loop from an output portion thereof to an input portion thereof and having an oscillating frequency controlled by a control voltage corresponding to a phase difference between said external clock signal and said internal clock signal;
a read clock generator for generating a read clock signal from said internal clock signal for external outputting when data is read, said read clock generator including a variable delay circuit having a same structure as said voltage controlled oscillator except for said feedback loop and receiving a signal corresponding to said internal clock signal at an input portion thereof; and
a vernier setting circuit for setting a delay amount of said variable delay circuit in accordance with an external command.
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Abstract
A voltage controlled delay circuit having the same structure, except for a loop, as a voltage controlled oscillator included in a PLL circuit which in turn generates an internal clock signal from an external clock signal is controlled by a control voltage from the PLL circuit, and the delay output of the voltage controlled delay circuit is selected by a selection circuit in accordance with the output signal of a vernier-adjusting counter in order to generate a read clock signal. Therefore, a vernier for optimizing data input timing in a controller can be realized which always has a constant delay amount regardless of a change in operating environment.
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9 Claims
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1. A synchronous type semiconductor memory device, comprising:
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a phase synchronization circuit for generating an internal clock signal synchronized in phase with an externally supplied external clock signal, said phase synchronization circuit including a voltage controlled oscillator having a feedback loop from an output portion thereof to an input portion thereof and having an oscillating frequency controlled by a control voltage corresponding to a phase difference between said external clock signal and said internal clock signal; a read clock generator for generating a read clock signal from said internal clock signal for external outputting when data is read, said read clock generator including a variable delay circuit having a same structure as said voltage controlled oscillator except for said feedback loop and receiving a signal corresponding to said internal clock signal at an input portion thereof; and a vernier setting circuit for setting a delay amount of said variable delay circuit in accordance with an external command. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification