Delay circuit of delay locked loop having single and dual delay lines and control method of the same

A delay circuit in a delay locked loop includes a first delay circuit unit for delaying an input signal using a single delay line in response to first control signals and then outputting a first delay signal and a second delay signal, and a second delay circuit unit for delaying the first delay signal and the second delay signal by delay time, which is correspondent to second control signals and third control signals, using a dual delay line and then outputting a third delay signal and a fourth delay signal.

CROSS-REFERENCES TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. 119(a) to Korean application number 10-2007-0128301, filed on Dec. 11, 2007, in the Korean Intellectual Property Office, which is incorporated by reference in its entirety as if set forth in full.

BACKGROUND

1. Technical Field

The embodiments described herein relate to a semiconductor circuit technology and, more particularly, to a delay circuit of a delay locked loop in a semiconductor integrated circuit and a method for controlling the same.

2. Related Art

A delay locked loop (DLL) is a circuit for synchronizing a clock signal supplied from an external circuit with a clock signal used in an internal circuit of a conventional semiconductor memory apparatus. A conventional delay locked loop includes a delay circuit. The delay circuit changes a delay time of a clock signal, which is input from the external circuit, in response to a control signal, which is generated within the delay locked loop, and outputs the delayed clock signal. Conventional delay circuits are implemented by a dual delay line or a single delay line.

As shown inFIG. 1, a conventional delay circuit includes a dual delay line (1and2) and a phase mixer3.

The dual delay line (1and2) delays and outputs a clock signal in response to control signals generated by shift registers in a delay locked loop. The delay time is determined by the number of unit delayers activated by the control signals.

The phase mixer3mixes two signals that are output by the dual delay line (1and2) to output an output signal ‘CLK_out’.

A driving circuit is required to drive signals input onto the two delay lines. However, a conventional driving circuit consumes a large amount of current and causes a large amount of noise. In addition, since the driving circuit occupies a large area, it limits integration.

Referring toFIG. 2, a delay circuit using a single delay line includes a plurality of delayers210to210to214and a plurality of switches215to219. The reference numeral220designate a multiplexer and230a phase mixer. U.S. Pat. No. 7,016,452 discloses a conventional delay circuit using the single delay line.

A delay circuit using the single delay line, such as that disclosed in U.S. Pat. No. 7,106,452, needs a large number of switches215to219to control the outputs of the plurality of delayers210to210to214. As a result, the circuit area becomes is increased and the circuit is unstable in coupling capacitance. In the delay circuit using the single delay line, the most critical issue is to increase the generation of signal distortion and then it is difficult to operate in a high-frequency.

SUMMARY

A delay circuit of a delay locked loop capable of stably operating in low and high frequency with a small-sized circuit area.

According to one aspect, a delay circuit in a delay locked loop comprises a first delay circuit unit for delaying an input signal using a single delay line in response to first control signals and then outputting a first delay signal and a second delay signal, and a second delay circuit unit for delaying the first delay signal and the second delay signal by a delay time, which corresponds to second control signals and third control signals, using a dual delay line and then outputting a third delay signal and a fourth delay signal.

According to another aspect, a method for controlling a delay circuit in a delay locked loop, wherein the delay circuit includes a first delay circuit unit and a second delay circuit unit, the method comprising controlling the delay circuit to fix a delay time of one of the first delay circuit unit and the second delay circuit unit, and executing a delay locking operation by varying a delay time of the other of the first delay circuit unit and the second delay circuit unit.

According to still another aspect, a method for controlling a delay circuit in a delay locked loop, wherein the delay circuit includes a first delay circuit unit and a second delay circuit unit, the method comprising executing a delay locking operation by varying a delay time of the second delay circuit unit in a state where a delay time of the first circuit unit is fixed, and varying the delay time of the first circuit unit when a delay is not locked by a maximum delay time of the second delay circuit unit.

According to still another aspect, a method for controlling a delay circuit in a delay locked loop, wherein the delay circuit includes a first delay circuit unit for outputting a first delay signal and a second delay signal by delaying an input signal and a second delay circuit unit for outputting a third delay signal and a fourth delay signal by delaying the first delay signal and the second delay signal, the method comprising outputting the first delay signal and the second delay signal in a state where a delay time of the first delay circuit unit is fixed, executing a delay locking operation by varying a delay time of the second delay circuit unit to output the third delay signal and the fourth delay signal, and varying the delay time of the first circuit unit when a delay is not locked by a maximum delay time of the second delay circuit unit.

DETAILED DESCRIPTION

FIG. 3is a diagram illustrating a delay circuit101according to one embodiment. As shown inFIG. 3, the delay circuit101, which can be included in a delay locked loop, can include a first delay circuit unit100, a second delay circuit unit200, and a phase mixer300.

The first delay circuit unit100can be configured to output a first delay signal ‘CLK_in_dlyU1’ and a second delay signal ‘CLK_in_dlyL1’, which are generated by delaying an input signal ‘CLK_in’ in response to first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’. The delay time of the first delay signal ‘CLK_in_dlyU1’ can be different from that of the second delay signal ‘CLK_in_dlyL1’.

The first delay circuit unit100can include a single delay line110, which can have a plurality of unit delayers UD1and a plurality of switches SW coupled to the plurality of unit delayers UD1, respectively.

The plurality of switches SW can be configured to output the first delay signal ‘CLK_in_dlyU1’ and the second delay signal ‘CLK_in_dlyL1’ using output signals of the first unit delayers UD1, which are respectively coupled to the switches SW, in response to the first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’.

The first delay signal ‘CLK_in_dlyU1’ can be output through a switch SW, which is turned on in respond to the first control signals ‘Sr0’, ‘Sr1’. ‘Sr2’, ‘Sr3’ and ‘Sr4’, of the plurality of switches SW.

The second delay signal ‘CLK_in_dlyL1’ can be output through a switch SW, which can be turned on in respond to the first control signals ‘Sf0’, ‘Sf1’. ‘Sf2’ and ‘Sf3’, of the plurality of switches SW.

The second delay circuit unit200can be configured to output a third delay signal ‘CLK_in_dlyU2’ and a fourth delay signal ‘CLK_in_dlyL2’ by delaying the output signal of the first delay circuit unit100for a predetermined time corresponding to second control signals ‘SU0’ to ‘SU4’ and third control signals ‘SL0’ to ‘SL4’.

The second delay circuit unit200can include a dual delay line which has a first delay line210and a second delay line220. The first delay line210can have the same configuration as the second delay line220and each of the first and second delay lines210and220can have a plurality of unit delayers US2.

As shown inFIG. 4, the first delay line210can include the plurality of unit delayers US2and a plurality of NAND gates ND1to ND6.

While the second unit delayers UD2can be implemented in a variety of ways,FIG. 4illustrated an example implementation comprising a combination of the two-NAND gates.

The plurality of NAND gates ND2to ND6, which receive the first delay signal ‘CLK_in_dlyU1’ input the received first delay signal ‘CLK_in_dlyU1’ into the second unit delayers UD2in response to second control signals ‘SU0’ to ‘SU4’. The NAND gate ND1inverts an output of the second unit delayer UD2at the final stage so that the third delay signal ‘CLK_in_dlyU2’ can be in phase with the first delay signal ‘CLK_in_dlyU1’. The third delay signal ‘CLK_in_dlyU2’ can be output with a delay time which is taken from a timing the first delay signal ‘CLK_in_dlyU1’ can be input into the second unit delayer UD2at the first stage when the output of the unit delayer UD2is output at the final stage.

The phase mixer300can be configured to output an output signal ‘CLK_out’ by mixing the third and fourth delay signals ‘CLK_in_dlyU2’ and ‘CLK_in_dlyL2’.

There can be a delay time between the first delay signal ‘CLK_in_dlyU1’ and the second delay signal ‘CLK_in_dlyL1’, and the delay time can correspond to at least one unit delayer UD1.

Generally, the delay locked loop101can include a phase detector to generate a detection signal by detecting a phase difference between an input signal ‘CLK_in’ and the output signal ‘CLK_out’, a counter to output count signals in response to the detection signal, and a decoder to generate a control signal for the delay circuit (single delay line or dual delay line) by decoding the counter signals. The first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’ and the second control signals ‘SU0’ to ‘SU4’ to control the first delay circuit unit100and the second delay circuit unit200can be generated by using this decoder of the delay locked loop.

The number and size of the first unit delayers UD1and the second unit delayers UD2can be different and can be determined based on the requirements of a particular implementation, such as the circuit design and the operating frequency.

A delay circuit according101can be a hybrid type design. That is, the first delay circuit unit100having the single delay line110can be provided at an input side and the second delay circuit unit200having the dual delay line of the first and second delay lines210and220can be provided at an output side.

A conventional delay circuit using only the dual delay line needs a large amount of current to drive the input signal ‘CLK_in’ input into two delay lines and causes a large amount of noise. However, a delay circuit configured as described herein can reduce the current consumption and noise by providing the first delay circuit unit100having the single delay line110to the input side. Since the input signal ‘CLK_in’ is provided to only the single delay line, the current consumption and the noise of the driver, which drives the input signal ‘CLK_in’, can be reduced.

Further, a conventional delay circuit using only the single delay line includes a large number of switches to multiplex the output signal. Accordingly, since a conventional delay circuit using only the single delay line causes a signal distortion, it is difficult to operate in the high frequency. However, a delay circuit configured according to the embodiments described herein can improve the high-frequency characteristics by providing the dual delay line (210and220), which does not need the switches for multiplexing the output signal, to the output side.

A delay circuit configured as described herein can be a hybrid-type delay circuit having two kinds of delay lines. The single delay line110can be designed with the reduction of the number of unit delayers, as compared with the conventional single line. Accordingly, the number of switches to transfer the output signals of the unit delayers is also reduced. The dual delay line (210and220) can be designed with the reduced number of unit delayers, as compared with the conventional dual delay line ofFIG. 1.

Even if a delay circuit configured as described herein is configured to have two kinds of delay lines, the total area is reduced, as compared with the conventional delay line ofFIG. 2. Since the number of switches in the first delay circuit unit100is reduced, the degradation of capacitance characteristics, which is caused by the plurality of switches, can also be overcome.

A method for controlling the delay circuit of the delay locked loop configured as described herein will now be described in detail.

The delay circuit101makes it possible to selectively operate the first delay circuit unit100or the second delay circuit unit200using the first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’, the second control signals ‘SU0’ to ‘SU4’ and the third control signals ‘SL0’ to ‘SL4’.

As mentioned above, the values of the first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’, the second control signals ‘SU0’ to ‘SU4’ and the third control signals ‘SL0’ to ‘SL4’ are generated and adjusted according to the internal construction of the delay locked loop.

In case that only the delay circuit unit100operates, the second control signals SU0to SU4and the third control signals SL0to SL4are fixed to a specific value and the first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’ are varied.

The values of the first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’ are adjusted until the delay locking operation has been completed.

The single delay110delays the input signal ‘CLK_in’ by a delay time which is varied according to the values of the first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’ and then outputs the first delay signal ‘CLK_in_dlyU1’ and the second delay signal ‘CLK_in_dlyL1’ to the dual delay line (210and220).

Since the second control signals ‘SU0’ to ‘SU4’ and the third control signals SL0to SL4are fixed to a specific value, the dual delay line (210and220) delays the first delay signal ‘CLK_in_dlyU1’ and the second delay signal ‘CLK_in_dlyL1’ by a specific delay time and then outputs the third delay signal ‘CLK_in_dlyU2’ and the fourth delay signal ‘CLK_in_dlyL2’ to the phase mixer300.

In case that only the second delay circuit unit200operates, the first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’ are fixed to a specific value and the second control signals ‘SU0’ to ‘SU4’ and the third control signals ‘SL0to ‘SL4’ are varied.

Since first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’ are fixed to a specific value, the single delay line110delays the input signal ‘CLK_in’ by a specific delay time and then outputs the first delay signal ‘CLK_in_dlyU1’ and the second delay signal ‘CLK_in_dlyL1’ to the dual delay line (210and220).

The values of the second control signals ‘SU0’ to ‘SU4’ and the third control signals ‘SL0’ to ‘SL4’ are adjusted until the delay locking operation has been completed.

Accordingly, the first and second delay circuit units100and200are controlled selectively or in batch processing so that different delay values can be provided.

The dual delay line (210and220) varies the delay time of the first delay signal ‘CLK_in_dlyU1’ and the second delay signal ‘CLK_in_dlyL1’ in response to the second control signals SU0to SU4and the third control signals SL0to SL4and then outputs the third delay signal ‘CLK_in_dlyU2’ and the fourth delay signal ‘CLK_in_dlyL2’ to the phase mixer300.

The case where only the second delay circuit unit200operates is shown inFIG. 5. Initially, the first delay circuit unit100outputs the first delay signal ‘CLK_in_dlyU1’ and the second delay signal ‘CLK_in_dlyL1’, by fixing the first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’ to a specific delay value and delaying the input signal ‘CLK_in’ by a specific delay time.

The first line210of the dual delay line only varies the delay time of the first delay signal ‘CLK_in_dlyU1’ according to the second control signals ‘SU0’ to ‘SU4’ and outputs the third delay signal ‘CLK_in_dlyU2’

Since the delay is locked after the increasing of the delay time (B) corresponding to two unit delayers UD2, which are taken from the initial unit delayer UD2(A), it is not required to operate the first delay circuit unit100.

Meanwhile, a delay circuit configured as described herein makes it possible to achieve the locking operation in the delay locked loop by operating the first delay circuit unit100and the second delay circuit unit200in a predetermined order. In case that the delay locking is not achieved by the maximum delay time of the dual delay line (210and220) in the second delay circuit unit200, the first circuit unit100executes the delay locking operation and this operation will be described inFIG. 6.

Initially, the first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’ are fixed to a specific value in order that the first delay signal ‘CLK_in_dlyU1’ and the second signal ‘CLK_in_dlyL1’ have a minimum delay time.

Accordingly, the first circuit unit100outputs the first delay signal ‘CLK_in_dlyU1’, which has the minimum delay time corresponding to the delay time of one unit delayer UD1. Furthermore, the first circuit unit100outputs the second delay signal ‘CLK_in_dlyL1’ which has a delay time corresponding to two unit delayers UD1.

Next, the dual delay line (210and220) changes the first delay signal ‘CLK_in_dlyU1’ and the second delay signal ‘CLK_in_dlyL1’ into the third delay signal ‘CLK_in_dlyU2’ and the fourth delay signal ‘CLK_in_dlyL2’, by adjusting the second control signals ‘SU0’ to ‘SU4’ and the third control signals ‘SL0’ to ‘SL4’, respectively.

Since the delay is not locked by the maximum delay time of the dual delay line (210and220), the second control signals ‘SU0’ to ‘SU4’ and the third control signals ‘SL0’ to ‘SL4’ are fixed and the first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’ are adjusted.

The single delay line110delays the input signal ‘CLK_in’ by a variable delay time according to the first control signals ‘Sr0’, ‘Sf0’, . . . , ‘Sf3’ and ‘Sr4’, thereby outputting the first delay signal ‘CLK_in_dlyU1’ and the second delay signal ‘CLK_in_dlyL1’.

The dual delay line (210and220) delays the first delay signal ‘CLK_in_dlyU1’ and the second delay signal ‘CLK_in_dlyL1’ by the maximum delay time and then outputs the third delay signal ‘CLK_in_dlyU2’ and the fourth delay signal ‘CLK_in_dlyL2’ to the phase mixer300.

The delay is locked after the delay time (D) corresponding to two unit delayers UD1which are taken from the initial unit delayer UD1(C).

While certain embodiments have been described above, it will be understood that the embodiments described are by way of example only. For example, the delay locking operation is executed by varying the delay time in the first delay circuit unit100. That is, in case that the delay is not locked by the maximum delay time in the first delay circuit unit100, the delay time of the second delay circuit unit200can be varied. Accordingly, the apparatus and methods described herein should not be limited based on the described embodiments. Rather, the apparatus and methods described herein should only be limited in light of the claims that follow when taken in conjunction with the above description and accompanying drawings.