Devices for synchronizing clock signals

1. A device for synchronizing clock signals comprising:

a first delay unit with variably controllable delay time, an input of the first delay unit being connected to an output of an input circuit having a first delay time, the input circuit receiving a first clock signal, wherein the first delay unit outputs at its output a second clock signal that is to be synchronized with the first clock signal;

a second delay unit having a fixed delay time portion corresponding approximately to the first delay time, and an additional variably controllable delay time portion, and which is connected at its input to the output of the first delay unit;

a first phase comparison unit, a first input of which is connected to the output of the input circuit, and a second input of which is connected to an output of the second delay unit, and an output signal of which controls the delay time of the first delay unit;

a copy of the input circuit, an input of which is connected to the output of the first delay unit; and

a second phase comparison unit, a first input of which is connected to the output of the input circuit, and a second input of which is connected to an output of the copy of the input circuit, and an output signal of which controls the variable delay time portion of the second delay unit.

2. The device according to claim 1 , further comprising an output circuit with a further delay time, the output circuit being connected between the output of the first delay unit and the input of the copy of the input circuit, and outputting at its output the second clock signal that is to be synchronized with the first clock signal, wherein the fixed delay time portion of the second delay unit corresponds approximately to a sum of the first delay time and a further delay time.

3. The device according to claim 1 , wherein the output at which the second clock signal is generated is connected to an ohm resistive and/or capacitive load.

4. The device according to claim 1 , further comprising an output circuit with a further delay time, the output circuit including of one or a plurality of first circuit stages and one last circuit stage which outputs at its output the second clock signal and which is connected to a load, wherein the plurality of first circuit stages is connected between the output of the first delay unit and, by interconnecting a copy of the last circuit stage, the input of the copy of the input circuit, wherein the fixed delay time portion of the second delay unit corresponds approximately to the sum of the first delay time and a further delay time.

5. The device according to claim 1 , the device being designed in the form of an integrated circuit chip.

6. The device according to claim 5 , wherein the first clock signal originates from a device connected to the chip.

7. The device according to claim 6 , wherein the second clock signal is output by the chip to the device.

8. The device according to claim 2 , wherein the output circuit includes an off-chip-driver.

9. The device according to claim 1 , wherein the input circuit includes a receiver.

10. The device according to claim 9 , wherein the receiver includes a differential amplifier.

11. The device according to claim 1 , wherein the first phase comparison unit and the second phase comparison unit each include a phase detector.

12. A semiconductor memory comprising a device according to any of claim 1 .

13. The semiconductor memory according to claim 12 , wherein the semiconductor memory is a DDR-SDRAM.