KR20060077172A - Delay locked loop for multi-phase clock output - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor circuit design techniques, and more particularly, to a delayed synchronization loop, and more particularly, to a delayed synchronization loop for multiphase clock output. SUMMARY OF THE INVENTION An object of the present invention is to provide a delayed synchronization loop for outputting a multi-phase clock capable of generating a clock having a desired phase by preventing malfunction due to harmonic locks while minimizing an increase in chip area and current consumption. In delayed synchronous loop, the harmonic lock state occurs when the phase of delay clock has a phase difference of more than 360 ° compared to the reference clock. Therefore, delay delay loop is performed after artificially making the initial phase difference less than 360 °. When activated, harmonic locks can be prevented. Therefore, in the present invention, in the initial lock tracking section of the delayed synchronization loop, the multi-phase clock generator operates as an oscillator so that the entire system is operated as a phase-locked loop, thereby narrowing the phase difference between the output clock and the input clock to 360 ° or less, and then precise locking. For operation only, the multi-phase clock generator operates as a natural phase delay and the entire system operates as a delayed synchronization loop.

Multi-phase Clock, Delay-Sync Loop, Phase-Lock Loop, Harmonic Lock State, Phase Detector

Description

DELAY LOCKED LOOP FOR MULTI-PHASE CLOCK OUTPUT}             

1 is a block diagram of a delayed synchronization loop for multi-phase clock output according to the prior art.

FIG. 2 is a timing diagram showing a waveform of a clock outputted in the normal locked state of the conventional delayed synchronization loop for multi-phase clock output shown in FIG.

3 is a timing diagram showing a waveform of a clock outputted in a harmonic locked state by the conventional delayed synchronization loop for multi-phase clock output shown in FIG.

4 is a block diagram of a delayed synchronization loop for multi-phase clock output according to an embodiment of the present invention.

5 is an output frequency characteristic diagram of a delayed synchronization loop according to the present invention.

* Explanation of symbols for the main parts of the drawings

110: phase comparator

120: charge pump

130: loop filter                 

140: clock generator

150: phase detector

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor circuit design techniques, and more particularly, to a delayed synchronization loop, and more particularly, to a delayed synchronization loop for multiphase clock output.

Low voltage differential signaling (LVDS) is one of the signal transmission methods for interface between a host computer and a monitor in a flat panel display. In the case of using this transmission method, the transmitting end transmits 7 serial data in synchronization with one clock to the receiving end, and the receiving end has a serial-to-parallel converter (SPC) for converting the serial data into parallel data. In such a serial-to-parallel converter, data conversion is performed using seven clocks having different phases.

In order to generate a plurality of clocks out of phase with each other, a phase locked loop or a delay locked loop is generally used. Among them, the delayed synchronous loop is a more preferred trend due to the advantage of having a smaller jitter characteristic than the phase synchronous loop, but has a disadvantage of being in a harmonic lock state due to the limitation of the phase capture range.

The output clocks of the delayed synchronous loop have a constant phase relationship with the input clock, which means that the output clock of the delayed synchronous loop can be easily synchronized at an unwanted multiple of 360 ° with respect to the input clock. For example, it is assumed that the phase difference between the output clock and the input clock as the phase comparison target is 360 ° and the desired phases of the output clock are 90 °, 180 ° and 270 °, respectively. However, if the delayed synchronization loop is synchronized at 720 °, which is an incorrect integer multiple of 360 °, the phases of the output clocks are 180 °, 360 °, and 540 °, respectively, rather than the desired phases. This case is called a harmonic lock state.

1 is a block diagram of a delayed synchronization loop for multi-phase clock output according to the prior art.

Referring to FIG. 1, a delay synchronization loop for outputting a multi-phase clock according to the related art includes a phase comparator 10 and a phase comparator 10 for comparing phases of a reference clock CLK_REF and a feedback delay clock CLK_D. The charge pump 20 performs a charge pumping operation in response to the output signals UP and DOWN, and a loop filter for rectifying the output voltage V1 of the charge pump 20-AC voltage-to DC. 30) and a delay time is controlled according to the output voltage of the loop filter 30, and comprises a clock generator 40 for generating N multi-phase clocks phi_0, phi_1, ..., phi_N having a constant phase difference. do.

Here, the clock generator 40 is composed of a delay chain in which a plurality of delay cells are connected in series.

The delayed synchronization loop for the multi-phase clock output configured as described above periodically compares the phases of the reference clock CLK_REF and the delay clock CLK_D, and becomes locked only when the rising edges of the two clocks coincide.                         

FIG. 2 is a timing diagram illustrating a waveform of a clock output by the conventional delayed synchronization loop for multi-phase clock output shown in FIG. 1 in a normally locked state, and the phase of the multi-phase clocks phi_0, phi_1,..., Phi_N is referenced. 90 °, 180 °,… with clock CLK_REF. 270 °, all within 360 ° range.

On the other hand, as shown in FIG. 3, even in the harmonic lock state, the rising edges of the reference clock CLK_REF and the delay clock CLK_D coincide with each other, and the delay synchronization loop does not distinguish it from the normal lock state and determines the lock state. Done. In this case, the phases of the multi-phase clocks phi_0, phi_1, ..., phi_N are 180 °, 360 °,... With the reference clock CLK_REF. In other words, it is distributed within the range of 540 ° to 720 °.

This harmonic lock has a problem of causing a malfunction of a system using a multi-phase clock.

In order to solve this problem, a delayed loop for multi-phase clock output with a double loop structure has been proposed. However, this technique requires an auxiliary phase delayer and an auxiliary charge pump. See IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL.39.NO.11., NOVEMBER 2004, "A Reset-Free Anti-Harmonic Delay-Locked Loop Using a Cycle Period Detector."

The present invention has been proposed to solve the above problems of the prior art, for minimizing the increase of chip area and current consumption while preventing the malfunction due to the harmonic lock for multi-phase clock output for generating a clock of the desired phase The purpose is to provide a delayed synchronization loop.

According to an aspect of the present invention for achieving the above technical problem, phase comparison means for comparing the phase of the reference clock and the delayed clock delay; Charge pumping means for performing a charge pumping operation in response to an output signal of the phase comparing means; Rectifying means for rectifying the output voltage of said charge pumping means; Phase detection means for detecting a phase difference between the reference clock and the delay clock to generate a phase difference detection signal indicating whether the phase difference is less than or equal to 360 °; And a clock generator for operating an oscillator or a phase delayer in response to the phase difference detection signal, the delay time being controlled according to the output voltage of the rectifying means, and generating N multiple phase clocks having a constant phase difference. A delayed synchronous loop for multiphase clock output is provided.

Preferably, the clock generating means, the delay chain is a plurality of delay cells are connected in series; First switching means for switching the input of the reference clock to the delay chain in response to a first phase difference detection signal; And second switching means for switching between an input terminal and an output terminal of the delay chain in response to a second phase difference detection signal, which is logically inversely related to the first phase difference detection signal.

In delayed synchronous loop, the harmonic lock state occurs when the phase of delay clock has a phase difference of more than 360 ° compared to the reference clock. Therefore, delay delay loop is performed after artificially making the initial phase difference less than 360 °. When activated, harmonic locks can be prevented. Therefore, in the present invention, in the initial lock tracking section of the delayed synchronization loop, the multi-phase clock generator operates as an oscillator so that the entire system is operated as a phase-locked loop, thereby narrowing the phase difference between the output clock and the input clock to 360 ° or less, and then precise locking. For operation only, the multi-phase clock generator operates as a natural phase delay and the entire system operates as a delayed synchronization loop.

Hereinafter, preferred embodiments of the present invention will be introduced in order to enable those skilled in the art to more easily carry out the present invention.

4 is a block diagram of a delay synchronization loop for outputting a multi-phase clock according to an embodiment of the present invention.

Referring to FIG. 4, a delay synchronization loop for outputting a multi-phase clock according to the present embodiment includes a phase comparator 110 and a phase comparator 110 for comparing phases of a reference clock CLK_REF and a feedback delay clock CLK_D. A loop filter for rectifying the charge pump 120 performing the charge pumping operation in response to the output signals UP and DOWN, and the output voltage V1 of the charge pump 120-AC voltage-to DC. And a phase detector 150 for detecting a phase difference between the reference clock CLK_REF and the delay clock CLK_D and generating phase difference detection signals DL and PL indicating whether the phase difference is 360 ° or less or more than 360 °. And the delay time is controlled according to the output voltage of the oscillator or the phase delayer-loop filter 130 in response to the phase difference detection signals DL and PL, and the N multiple phase clocks phi_0 and phi_1 have a constant phase difference. Generate a phi_N).

Here, the clock generator 140 includes a delay chain in which a plurality of delay cells are connected in series.

Meanwhile, the selective operation of the clock generator 140 is performed by the switching operation of the switches sw2 and sw1 controlled by the phase difference detection signals DL and PL, and the switch controlled by the phase delay mode signal DL ( sw2 is inserted into the reference clock CLK_REF input terminal of the clock generator 140 to switch the input of the reference clock CLK_REF, and the switch sw1 controlled by the oscillator mode signal PL is a loop of the clock generator 140. It is inserted between the filter output signal input terminal and the output terminal to perform a switching operation.

When the reference clock CLK_REF is input, the phase comparator 110 compares the phase of the random clock CLK_D selected from the output clocks phi_0, phi_1,..., Phi_N of the clock generator 140 with the reference clock CLK_REF. A signal UP and DOWN having a pulse width corresponding to the phase difference between the two clocks is output. Meanwhile, the charge pump 120 receiving the output signals UP and DOWN of the phase comparator 110 performs a charge pumping operation according to the pulse width of the corresponding signals UP and DOWN to the capacitor of the loop filter 130. The amount of charge charged is increased or decreased, and the loop filter 130 rectifies the amount of charge to a DC voltage.

On the other hand, the output voltage level of the loop filter 130 controls the phase of the output clock of the clock generator 140, one of the output clocks (phi_0, phi_1, ..., phi_N) is a phase comparator as the delay clock (CLK_D) It is fed back to 110. This continuous feedback operation is repeated when the pulse widths of the output signals UP and DOWN of the phase comparator 110 coincide, that is, until the delay clock CLK_D and the reference clock CLK_REF coincide.

The above operation is a general operation in a state in which there is no phase sensor 150 added in the present invention. Hereinafter, an operation according to the addition of the phase sensor 150 will be described.

The phase detector 150 determines whether the phase difference between the delay clock CLK_D and the reference clock CLK_REF output from the clock generator is greater than or equal to 360 °, and when the phase difference between the two clocks exceeds 360 °, the oscillator mode signal PL ) Is activated at a logic level high, and the phase delay mode signal DL is activated at a logic level high when the phase difference between the two clocks is 360 ° or less. Since the two phase difference detection signals DL and PL output from the phase detector 150 have a logical inversion relationship, when one of them is activated, the other one is inactivated.

When the phase difference between the delay clock CLK_D and the reference clock CLK_REF is greater than 360 °, the switch sw1 is turned on and the switch sw2 is turned off because the oscillator mode signal PL is activated to a logic level high. Therefore, the clock generator 140 operates as an oscillator, and the entire circuit operates as a phase locked loop to make the phase difference between the delay clock CLK_D and the reference clock CLK_REF 360 ° or less.

As such, when the phase difference between the delay clock CLK_D and the reference clock CLK_REF is 360 ° or less, the phase delay mode signal DL is activated to a logic level high, so that the switch sw1 is turned off and the switch sw2 is turned on. Therefore, the clock generator 140 operates as a phase delay, and the entire circuit operates as a delay synchronization loop to narrow the phase difference between the delay clock CLK_D and the reference clock CLK_REF.

Thereafter, the phase detector 150 continuously detects the phase difference between the delay clock CLK_D and the reference clock CLK_REF, and causes the entire circuit to operate as a phase-locked loop or a delay-locked loop according to the phase difference between the two clocks.

5 is a diagram illustrating an output frequency characteristic of a delayed synchronization loop according to the present invention, and illustrates a process in which the delayed synchronization loop is locked to the loop filter voltage on the assumption that the target output frequency is 100 MHz.

In the case of operating only as a delay synchronous loop until the entire circuit is locked to 100 MHz as in the prior art, there is a risk of harmonic lock at 25 MHz and 50 MHz, but the delay synchronous loop according to the present invention operates as a phase synchronous loop at 25 MHz and 50 MHz. It can fundamentally prevent locks.

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

The present invention described above has the effect of suppressing the malfunction of the system by preventing the harmonic lock of the delayed synchronization loop for multi-phase clock output. In addition, compared to the conventional double loop structure, the increase in chip area and current consumption is minimized.

Claims (2)

Phase comparison means for comparing a phase of the reference clock and the delayed delayed clock; Charge pumping means for performing a charge pumping operation in response to an output signal of the phase comparing means; Rectifying means for rectifying the output voltage of said charge pumping means; Phase detection means for detecting a phase difference between the reference clock and the delay clock to generate a phase difference detection signal indicating whether the phase difference is less than or equal to 360 °; And An oscillator or phase delay in response to the phase difference detection signal, the delay time being controlled according to the output voltage of the rectifying means and generating N multi-phase clocks having a constant phase difference; A delayed synchronization loop for outputting a multi-phase clock having: The method of claim 1, The clock generating means, A delay chain having a plurality of delay cells connected in series; First switching means for switching the input of the reference clock to the delay chain in response to a first phase difference detection signal; And And second switching means for switching between an input terminal and an output terminal of said delay chain in response to a second phase difference detection signal, said logic being inversely related to said first phase difference detection signal. Synchronous loop.

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