Delay locked loop

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a delay locked loop. More specifically, the invention relates to a voltage control delay loop (VCDL) forming a delay locked loop (DLL).

Description of the Prior Art

In the field of high-speed data communication, synchronization of data and a clock to be inputted has been an important technique.

For example, in a synchronization system in the field of high-speed data communication having a data transfer speed exceeding 2 gigabits/sec (Gbps), as one of means for uniformalizing the edges of a clock input and a data input, a DLL is used to cancel propagation delay time in a buffer of a clock tree circuit (CT) in a chip (IC).

As shown in FIG. 4, the DLL has a clock receiver 1 receiving a clock of 1.25 GHz inputted from a clock (CL) terminal; a delay circuit part 15 having n delay elements 16 connected in series for input and sequential delay of a reception clock (A) outputted from the clock receiver 1; a clock tree (CT) part 6 creating clocks (B) with the same timing based on an output of delay circuit part 15; a phase control part 7 performing phase-control by the reception clock (A) and the clock (B) from the CT6 to on/off control the delay elements 16 of delay circuit parr 15; data receivers 8, 9 receiving data of 2.5 Gbps inputted from data input terminals (D0 to D15); and flip-flops (F/Fs) 10, 11 storing the data by reception outputs (C) of the data receivers 8, 9 and the clocks (B) from CT part 6. The phase control part 7 is represented in one block, and has functions of phase detect, charge pump and low-pass filter. Only the two data receivers 8, 9 and only the two F/Fs 10, 11 are shown. The data receivers 8, 9 and the F/Fs 10, 11 are naturally provided corresponding to the number of the data input terminals.

Such DLL compensates for the clock delay variation of the CT part 6 by phase control part 7 and delay circuit part 15 and locks the clock (B). As shown in FIG. 5, the rising edge of the clock (B) to be synchronized with the data (C) after one cycle of the reception clock (A) is a lock point (LP) via the delay circuit part 15 and the CT part 6 in the DLL. In other words, the clock (B) is locked at the rising edge of the clock (B). The clock (A) of 1.25 GHz is at a speed of 800 picoseconds (ps) in one clock cycle so as to mean that the total delay time of delay circuit part 15 and CT part 6 is 800ps.

The data (C) is typically propagated in a timing delay 90 degrees in phase to the clock (A) . When the data receivers 8, 9 are of the same construction (shape) and have same performance, the timing shown in the drawing is maintained. For this reason, flip-flops (F/Fs) 10, 11 can reliably receive the data (C) by the clocks (B) (that is, clocks 0 to 15) with the same timing.

As shown in FIG. 6, the basic circuit of the delay circuit part and the CT part 6 has differential NMOS transistors 20, 21 having gates to which clock input IN and IN inversion are supplied; load elements 17, 18 connected between the NMOSs 20, 21 and a power source VDD; and a constant current source 19 connected between the NMOSs 20, 21 and a ground GND. Clock output OUT and OUT inversion are taken out from the junctions of NMOS transistors 21, 20 and load elements 18, 17.

When the basic circuit is used in the delay elements 16 of delay circuit part 15, phase control part 7 variably controls the constant current source 19. The delay time of delay circuit part 15 can be thus varied. As load elements 17, 18 in the case of delay circuit part 15, an active load of the NMOS transistor and a resistance load of high-resistance polysilicon are used. As load elements 17, 18 in the case of clock tree (CT) part 6, a resistance lead of high-resistance polysilicon is used.

The delay time of the above-mentioned prior art delay locked loop, particularly, the delay time of the clock tree (CT) part, largely depends on variation in the resistance elements forming the resistance loads.

When attempting to compensate for delay for the variation in the resistance elements only by a delay variation width generated by a current change of the current source of the delay circuit part, the resistance elements are return-controlled at the same time. A sufficient variation width cannot be compensated. As a result, a clock outputted from the CT part to the data processing part side cannot be locked. In other words, the lock point of the data and the clock cannot be determined.

BRIEF SUMMARY OF THE INVENTION

Objects of the Invention

An object of the invention is to provide a delay locked loop which can compensate for delay time of a clock tree (CT) part only by a delay variation width of delay elements of a delay circuit part.

Summary of the Invention

A delay locked loop of the invention which synthesizes data and a clock inputted from outside has: <ul id="ul0001" list-style="none" compact="compact"><li>voltage control delay loops having a plurality of delay circuit parts sequentially delaying the clock;</li><li>a slot selector selecting a slot outputted from the delay circuit parts of the voltage control delay loops;</li><li>a clock tree part creating a plurality of clocks with the same timing by an output of the slot selector;</li><li>a phase control part phase-controlling the plurality of delay circuit pares corresponding to the output clock delay variation of the clock tree part; and</li><li>sensing means on-off controlling all or part of the plurality of delay circuit parts and the slot selector.</li></ul>

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other objects, features and advantages of this invention will become more apparent by reference to the following detailed description of the invention taken in conjunction with the accompanying drawings, wherein: <ul id="ul0002" list-style="none" compact="compact"><li>FIG. 1 is a block diagram of a delay locked loop of assistance in explaining an embodiment of the invention;</li><li>FIG. 2 is a data and clock waveform chart of FIG. 1;</li><li>FIGS. 3A and 3B are diagrams showing a select signal generation circuit of FIG. 1 and its voltage and resistance features;</li><li>FIG. 4 is a block diagram of a delay locked loop showing an example of prior art;</li><li>FIG. 5 is a data and clock waveform chart of FIG. 4; and</li><li>FIG. 6 is a block diagram of the clock tree circuit shown in FIG. 4.</li></ul>

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the invention will be described below with reference to the drawings.

As shown in FIG. 1, a DLL of this embodiment has a clock receiver 1 receiving a clock of 1.25 GHz inputted from a clock (CL) terminal; a voltage control delay loop (VCDL) 2 having L delay elements 12 connected in series for input and sequential delay of a reception clock (A) outputted from the clock receiver 1 and outputting slot L by a phase control signal; a VCDL 3 having M delay elements 12 connected in series for input and sequential delay of the output of VCDL 2, that is, slot L and outputting slot M by the phase control signal and the later-described select signal S2; a VCDL 4 having N delay elements 12 connected in series for input and sequential delay of the output of VCDL 3, that is, slot M and outputting slot N by the phase control signal and the later-described select signal S1; a slot selector 5 selecting slots L, M and N outputted from the VCDLs 2 to 4 by the select signals S1, S2 and outputting the selected slot as a clock; a clock tree (CT) part 6 creating clocks (B) with the same timing by the clock of slot selector 5; a phase control part 7 performing phase-control by the reception clock (A) and the clock (B) from CT6 to on/off control delay elements 12 of VCDLs 2 to 4 for each group (L, M and N); data receivers 8, 9 as the data part circuit explained in FIG. 4; and flip-flops (F/Fs) 10, 11. Also in this embodiment, phase control part 7 is represented in one block as in the prior art of FIG. 4, and has functions of phase detect, charge pump and low-pass filter. Only the two data receivers 8, 9 and only the two F/Fs 10, 11 are shown. The data receivers 8, 9 and the F/Fs 10, 11 are naturally provided corresponding to the number of the data input terminals.

The DLL of this embodiment compensates for the clock delay variation of CT part 6 by phase control part 7, VCDLs 2 to 4, slot selector 5, and the generation means of the select signals S1, S2 as the sensing means to lock the clock (B).

In this embodiment, VCDLs 2 to 4 forming the DLL sense the resistance value variation of differential circuits of VCDLs 2 to 4 and CT part 6 consisting mainly of the resistance loads to determine the basic number of VCDLs 2 to 4 corresponding to the resistance value variation upon power-on. The basic number of the VCDLs 2 to 4 to be operated is fixedly held until the power is shut off. After the basic number of VCDLs 2 to 4 is held for change to the lock operation of clock (B), performing locking by desired delay time. As shown in FIG. 2, as in FIG. 5, the clock (B) delayed in one cycle (800 picoseconds) from the rising of the clock (A) received by clock receiver 1 is created. The point is a lock point (LP). As shown in FIG. 3A, the select signal generation circuit is used as the sensing means sensing the variation in load resistance (load resistance of the delay elements 12 in VCDLs 2 to 4, load resistance in CT part 6, or the resistance element described below). The construction is formed by a resistance element 13 having the same shape as the load resistance; a constant current source 12 supplying a constant current (a constant current not depending on resistance element 13) to resistance element 13; and a Schmidt comparator 14 comparing potential VCONT of the junction of resistance element 13 and constant current source 12 with threshold voltages V1, V2 and V3 (V3 &gt; V2 &gt; V1) as reference voltages having different values to output select signals S1, S2.

In such sensing means, when constant current is supplied to resistance element 13 having the same shape as the load resistance, the VCONT potential as one end of the input of Schmidt comparator 14 is varied to the electric potential corresponding to the resistance value of resistance element 13.

When the resistance value is made to be small, as shown in FIG. 3B, the VCONT is positioned between reference threshold voltages V1 and V2 and the delay time of clock tree part 6 and VCDLs 2 to 4 indicates a small value. At this time, select signals S1, S2 are both on and the VCDLs 2 to 4 are all operated to change the clock into the lock state.

When the resistance value is made in a center region, as shown in FIG. 3B, the VCONT is positioned between reference threshold voltages V2 and V3 and the delay time of clock tree part 6 and VCDLs 2 to 4 indicates an almost center value. At this time, only the select signal S1 is off and the VCDLs 2 and 3 are operated to change the clock into the lock state.

When the resistance value is made to be large, as shown in FIG. 3B, the VCONT is positioned above the reference threshold potential V3 and the delay time of clock tree part 6 and

VCDLs 2 to 4 indicates a large value. At this time, the select signals S1, S2 are both off and only VCDL 2 is operated to change the clock into the lock state.

Schmidt comparator 14 is used in a high-speed differential common mode logic (CML) circuit. The high-resistance polysilicon often used in the high-speed differential CML circuit has a very low temperature dependence. The resistance value of the resistance element once manufactured indicates an almost constant value during operation. In this embodiment, when such resistance element is used, a Schmidt circuit is provided so as to prevent the value of the potential VCONT from exceeding threshold voltages V2, V3 due to the influence of noise. In other words, when the power is once turned on and the potential VCONT exceeds the thresholdvoltage V3, select signals S1, S2 are prevented from being turned on unless the potential VCONT is below threshold voltage V1. As a result, when using Schmidt comparator 14, noise margin can be increased.

As described above, the delay locked loop of the present invention determines, upon power-on, the basic number of the plurality of VCDLs provided depending on the resistance value variation of the resistance loads. When the delay variation width of the VCDL is small, the clock of the clock tree (CT) part can be locked within the variation range . To put it briefly, the resistance value variation of the resistance loads of the VCDLs is sensed, and then, the basic number of the VCDLs is determined corresponding to the variation to lock the clock. Even when the delay variation width of the VCDLs is small, malfunction can be prevented.

Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that the appended claims will cover any modifications or embodiments as fall within the true scope of the invention.