Negatively Delayed Signal Generating Circuit for Compensating Duty Rate

1. Field of the Invention

The present invention relates to a negatively delayed signal generating circuit, and more particularly to an improved negatively delayed signal generating circuit for compensating a duty rate of an input signal.

2. Description of the Background Art

FIG. 1 is a circuit view illustrating a negatively delayed signal generating circuit according to the background art.

As shown therein, the negatively delayed signal generating circuit includes a pulse generator 10 for receiving an input signal CKIN and generating a oneshot pulse signal S1. A first delay unit 11 delays the oneshot pulse signal S1 and outputs a delayed oneshot pulse signal S2. A forward delay unit 12 includes a plurality of delay units for sequentially delaying the delayed oneshot pulse signal 32 output from the first delay unit 11. A mirror control unit 13 includes a plurality of NAND gates for respectively NANDing the oneshot pulse signal S1 and the sequentially delayed oneshot pulse signals, for example S3, output from the plurality of delay units in the forward delay unit 12, thereby outputting signals, for example, a signal S4. A backward delay unit 14 sequentially delays the output signal of the mirror control unit 13 and outputs a signal S5. A dummy load unit 15 receives output signals of the backward delay unit 14 and a ground voltage. A second delay unit 16 delays the output signal S5 of the backward delay unit 14 and outputs a negatively delayed signal CKO.

The pulse generator 10 includes an inverter I1 for inverting the input signal CKIN, a NAND gate ND1 for NANDing the input signal CKIN and the output signal of the inverter 11, and an inverter 12 for inverting the output signal of the NAND gate ND1.

The first delay unit 11 includes inverters 13,14 and buffers B1, B2 which are serially connected with one another.

The forward delay unit 12 includes a plurality of delay units D1, D2, . . . , D6 which are serially connected with one another. The delay unit D1 is provided with a NAND gate ND2 for NANDing the output signal S2 of the first delay unit 11 and a source voltage Vcc, and an inverter 15 for inverting the output signal of the NAND gate ND2. Also, the other delay units D2, D3, . . . , D6 are respectively identical to the first delay unit D1 in composition.

The mirror control unit 13 includes a plurality of NAND gates ND3, ND4, . . . , ND8, each of which NANDs the output signal S1 of the pulse generator 10 and a corresponding one of the output signals of the plurality of delay units D1, D2, . . . , D6 in the forward delay unit 12, thereby outputting the signals which are locked, for example, the signal S4.

The backward delay unit 14 includes a plurality of delay units D7, D8, . . . , D12 for sequentially delaying signals output from the mirror control unit 13. For example, the delay unit D12 includes a NAND gate ND9 and an inverter 16 to delay the output signal of the NAND gate ND8 in the mirror control unit 13, and output its delayed signal to the subsequent delay unit D11. Also, the other delay units D7, D8, . . . , D11 are respectively identical to the delay unit D12 in composition.

The dummy load unit 15 includes a plurality of NAND gates ND10A, ND10B, . . . , ND10F for respectively NANDing a corresponding one of the output signals of the delay units D7, D8, . . . , D12 in the backward delay unit 14 and a ground voltage.

The second delay unit 16 includes inverters 17, 18 for sequentially delaying the output signal of the backward delay unit 13.

With reference to FIGS. 2A through 2G illustrating timing diagrams of respective signals in the circuit of FIG. 1, the conventional negatively delayed signal generating circuit will now be described.

The pulse generator 10 that receives the input signal CKIN shown in FIG. 2A generates the oneshot pulse signal S1 in FIG. 2B having a pulse width PW1 and delayed as much as t1 by the inverters 11, 12, and outputs the generated oneshot pulse signal S1 to the first delay unit 11 and the mirror control unit 13.

The first delay unit 11 receives the oneshot pulse signal S1 and outputs the pulse signal S2 in FIG. 2C delayed as much as t2 to the forward delay unit 12.

Then, the plurality of delay units D1, D2, . . . , D6 in the forward delay unit 12 respectively, sequentially delay the output signal S2 of the first delay unit 11 as much as t3 to output the signal S2 in FIG. 2C.

When the oneshot pulse signal S1 of the pulse generator 10 and the respective output signals of the plurality of delay units D1, D2, . . . , D6 are in high levels at the same time, the respective NAND gates ND3, ND4, . . . , ND8 in the mirror control unit 13 respectively output a locked signal, for example, the signal S4 in FIG. 2E to the backward delay unit 14. Then, the backward delay unit 14 sequentially delays the locked signal and outputs the signal S5 in FIG. 2F to the second delay unit 16. The second delay unit 16 receives the signal S5 from the backward delay unit 14 and outputs the output signal CKO in FIG. 2G delayed as much as t4 compared to the signal S3 of the forward delay unit 12.

Therefore, the output signal CKO is converted to a locking signal during first and second cycles T1, T2 with regard to the input signal CK1, thereby becoming a negatively delayed signal slightly faster than a third pulse of the signal S1 in FIG. 2B beginning a third cycle T3.

Here, in order to generate the output signal CKO with its frequency larger than that of the input signal CKIN in the conventional negatively delayed signal generating circuit, respective rising and falling edges of the input signal CKIN need to be used. However, when the duty rate of the input signal is irregular, the duty rate of the negatively delayed signal also becomes irregular, whereby the conventional negatively delayed signal generating circuit for outputting the negatively delayed signal with its frequency larger than that of the input signal by detecting the rising and falling edges of the input signal is not applicable to a system that requires a high speed internal signal.

Accordingly, it is an object of the present invention to provide a negatively delayed signal generating circuit for compensating an input signal duty rate, wherein the negatively delayed signal is generated within two cycles of the input signal with its rising edge regarded as a reference, regardless of a duty rate of the input signal, and wherein the negatively delayed signal has a larger frequency than that of the input signal and its duty rate is close to 50%.

To achieve the above-described object, there is provided a negatively delayed signal generating circuit for compensating an input signal duty rate according to the present invention which includes a buffer for delaying an input signal and outputting a delayed signal, a forward delay unit including a pulse generator for receiving the delayed signal and generating an input pulse signal, and a plurality of delay units for sequentially delaying an output signal of the pulse generator, a latch unit for receiving the delayed signal as a first input signal, and respective output signals of the pulse generator and the plurality of delay units as second input signals, thereby outputting a plurality of latch signals, a first logic operation unit for receiving the plurality of latch signals and outputting locked latch signals, a second logic operation unit for operating the locked latch signals and the second input signals respectively delayed for more than one cycle with regard to the delayed signals, and outputting a plurality of first delay pulse signals which are locked and delayed over one cycle, a full wave backward delay unit for sequentially delaying the plurality of first delay pulse signals through the second logic operation unit, a third logic operation unit for outputting a plurality of second delay pulse signals respectively delayed for less than a half (1/2) cycle with regard to the locked latch signals and the delayed signals of the forward delay unit, a half wave backward delay unit for sequentially delaying the second delay pulse signals through the third logic operation unit, and a fourth logic operation unit for receiving respective output signals of the full wave backward delay unit and the half wave backward delay unit and outputting a negatively delayed signal.

The object and advantages of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific example, while indicating a preferred embodiment of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

The present invention will become better understood with reference to the accompanying drawings which are given only by way of illustration and thus are not limitative of the present invention, wherein:

FIG. 1 is a circuit view illustrating a conventional negatively delayed signal generating circuit;

FIGS. 2A through 2G are timing diagrams of respective signals in the circuit of FIG. 1;

FIG. 3 is a circuit view illustrating a negatively delayed signal generating circuit according to the present invention; and

FIGS. 4A through 4R are timing diagrams of respective signals in the circuit of FIG. 3.

With reference to the accompanying drawings, the negatively delayed signal generating circuit for compensating an input signal duty rate according to the present invention will now be described.

FIG. 3 is a circuit view illustrating a negatively delayed signal generating circuit according to the present invention. As shown therein, the negatively delayed signal generating circuit includes a buffer B3 for delaying an input signal CK and outputting a delayed signal BS3. A forward delay unit 21 includes a pulse generator A1 for receiving the delayed signal BS3 and generating a oneshot pulse signal AS1 having a pulse width of PW2, and a plurality of delay units A2, A3, . . . , A10 for sequentially delaying the oneshot pulse signal AS1. A latch unit 22 includes a plurality of D-type flipflops Fn (n=1, 2, . . . , 9), each of which receives a corresponding one of a plurality of output signals AS1, AS2, AS3, . . . , AS9 of the forward delay unit 21 and employs the delayed signal BS3 as their synchronous signals and then outputs a corresponding one of a plurality of latch signal pairs Q.sub.n, QB.sub.n (n=1, 2, . . . , 9). A first logic operation unit 23 includes NAND gates ND13, ND14, ND15 respectively connected to a corresponding one of inverters I12, I13, I14, wherein the NAND gates ND13, ND14, ND15 respectively NAND a corresponding one of the subordinate output signals QB.sub.n (n=7, 8, 9) and a corresponding one of the main output signals Q.sub.n-2 (n=7, 8, 9) of the D-type flipflops F.sub.n (n=1, 2, . . . , 9). A second logic operation unit 24 receives a corresponding one of the output signals SS1, SS2, SS3 of the first logic operation unit 23, and a delayed oneshot pulse signal, which corresponds to the timing at a rising edge of the delayed signal BS3, among the output signals AS1, AS2, . . . , AS9 of the forward delay unit 21. A full wave backward delay unit 25 includes a plurality of delay units C1, C2, . . . , C6 for sequentially delaying the output signals of the second logic operation unit 24. A third logic operation unit 26 includes a plurality of NAND gates ND19, ND20, . . . , ND24, each of which receives a corresponding one of the output signals SS1, SS2, SS3 of the first logic operation unit 23, and a corresponding one of the delayed oneshot pulse signals AS4, AS3, AS2 which pass through the delay units in the forward delay unit 21 to correspond to a half cycle of the delayed signal BS3. A half wave backward delay unit 27 includes a plurality of delay units E1, E2, . . . , E8 for sequentially delaying the respective output signals of the third logic operation unit 26.

The respective blocks will be explained in further detail.

The pulse generator Al and the delay units A2, A3, . . . , A10 in the forward delay unit 21 are provided with elements identical to those of the conventional pulse generator 10 and those of the delay units D1, D2, . . . , D6 in the conventional forward delay unit 11 in FIG. 1. That is, the pulse generator A1 includes inverters I9, I10 and a NAND gate ND11, and the delay unit A2, for example, in the forward delay unit 21 includes a NAND gate ND12 and an inverter I11.

The first logic operation unit 23 includes the NAND gates ND13, ND14, ND15 for respectively NANDing a corresponding one of the subordinate output signals QB.sub.n (n=7, 8, 9) and a corresponding one of the main output signals Q.sub.n-2 (n=7, 8, 9) of the D-type flipflops F.sub.n (n=1, 2, . . . , 9), and the inverters I12, I13, I14 for correspondingly inverting the output signals of the inverters I12, I13, I14 which in turn are to output the output signals SS1, SS2. SS3.

A second logic operation unit 24 includes the NAND gates ND16, ND17, ND18 for correspondingly NANDing the output signals SS1, SS2, SS3 of the first logic operation unit 23 and the delayed oneshot pulse signals AS8, AS9, AS10 received at the rising edge of the delayed signal BS3 among the output signals of the forward delay unit 21.

A full wave backward delay unit 25 includes a plurality of delay units C1, C2, . . . , C6 for sequentially delaying the output signals of the second logic operation unit 24. Here, the delay units C1, C2, . . . , C6 are arrayed identical to the delay units An (n=2, . . . , 10) in the forward delay unit 21, and the delay unit C1 includes a NAND gate ND19 for NANDing a source voltage Vcc and an output signal of the NAND gate ND18 in the second logic operation unit 24, and the inverter I15 for delaying the output signal of the NAND gate ND19.

A third logic operation unit 26 includes a plurality of NAND gates ND20, ND21, . . . , ND24 for correspondingly NANDing the output signals SS1, SS2, SS3 of the first logic operation unit 23 and the delayed oneshot pulse signals AS2, AS3, AS4 output from the forward delay unit 21 at a half cycle timing of the delayed signal BS3.

A half wave backward delay unit 27 includes a plurality of delay units E1, E2, . . . , E8 for sequentially delaying the respective output signals of the third logic operation unit 26. At this time, the delay unit E1 includes the NAND gate. ND25 and the inverter 116 in the same elements as the delay units A1, A2, . . . , A10 in the forward delay unit 21 and the delay units C1, C2, . . . , C6 in the full wave forward delay unit 25.

A fourth logic operation unit 28 includes a NAND gate ND26 for NANDing an output signal CS3 of the full wave backward delay unit 25 and an output signal ES5 of the half wave backward delay unit 27, and inverters 117, 118 for serially delaying the output signal of the NAND gate ND26.

With reference to FIGS. 4A through 4R, the operation of the negatively delayed signal generating circuit for compensating the input signal duty rate according to the present invention will now be described.

The buffer B3, as shown in FIG. 4A, delays the input signal CK, and outputs the delayed signal BS3 in FIG. 4B to the forward delay unit 21 and to the D-type flipflops F.sub.n (n=1, 2, . . . , 9) in the latch unit 22.

In the forward delay unit 21, when the pulse generator A1 generates the oneshot pulse signal AS1 having a predetermined width of PW2 shown in FIG. 4C, the delay units An (n=2, 3 . . . 10) sequentially delay the oneshot pulse signal as shown in FIGS. 4D through 41.

Here, eight oneshot pulse signals ASn (n=1, 2, . . . , 8) are included within one cycle of the delayed signal BS3, whereby eight of the delay units are employed. At the same time, the latch unit 22 receives the eight oneshot pulse signals AS1, AS2, . . . , AS8 and the output signal AS9 of the delay unit A9, and outputs the latch signal pairs QBn, Qn (n=1, 2, . . . , 9) to the first logic operation unit 23 in accordance with the synchronous signal BS3. At this time, the first logic operation unit 23 operates the output signals of the latch unit 22 to output the signals SS1, SS2, SS3.

The output signals SS1, SS2, SS3 of the first logic operation unit 23 and the oneshot pulse signals AS8, AS9, AS10 which are delayed over one cycle of the delayed signal BS3 are correspondingly NANDed in the second logic operation unit 24, and the output signals SS1, SS2, SS3 of the first logic operation unit 23 and the oneshot pulse signals AS2, AS3, AS4 which are delayed for a half (1/2) cycle of the delayed signal BS3 are correspondingly operated in the third logic operation unit 26.

That is, the second logic operation unit 24 serves to output the oneshot pulse signal AS8 delayed for one cycle, and the third logic operation unit 26 serves to output the oneshot pulse signal AS4 delayed for a half (1/2) cycle.

The second logic operation unit 24 correspondingly NANDs the output signals SS1, SS2, SS3 of the first logic operation unit 23 and the output signals AS8, AS9, AS10 of the forward delay unit 21 to thus output the operation results to the full wave backward delay unit 25. Then, the full wave backward delay unit 25, as shown in FIGS. 4K, 4L, 4M, and 4N, sequentially delays the operation results and output the signals CS1, CS2, SC3.

The third logic operation unit 26 correspondingly NANDs the output signals SS1, SS2, SS3 of the first logic operation unit 23 and the output signals AS2, AS3, AS4 of the forward delay unit 21 to thus output the operation results to the half wave backward delay unit 27, which in turn outputs the signals ES1, ES5, ES8 as shown in FIGS. 4O, 4P and 4Q.

At this time, the output signal CS3 of the full wave backward delay unit 25 denotes an output signal further delayed by the five delay units including two delay units A9, A10 of the forward delay unit 21 and three delay units C1, C2, C3 of the full wave backward delay unit 25. This is to eliminate the influence of time delay by the buffer B3 which generates the delayed signal BS3 but to be delayed in a negative base.

Likewise, the output signal ES5 of the half wave backward delay unit 27 also employs the five delay units En (n=1, 2, . . . , 5) of the half wave backward delay unit 27 in the same way as the output signal of the full wave backward delay unit 25 by the five delay units A9, A10, C1, C2, C3.

As show in FIG. 4R, the fourth logic operation unit 28 which has received the two output signals CS3, ES5 outputs the negatively delayed pulse signal CKI having a larger frequency than that of the input signal and a duty rate of 50%.

As described above, the negatively delayed signal generating circuit for compensating an input signal duty rate according to the present invention obtains a negatively delayed signal generated within two cycles of the input signal with its rising edge regarded as a reference, regardless of a duty rate of the input signal, wherein the negatively delayed signal has a larger frequency than that of the input signal and its duty rate is close to 50%, thereby being stably applicable to a semiconductor device requiring a high speed operation.

As the present invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, it should also be understood that the above-described embodiment is not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claim, and therefore all changes and modifications that fall within meets and bounds of the claim, or equivalences of such meets and bounds are therefore intended to embrace the appended claim.