Wide range multi-phase delay-locked loop
View Patent ↗A delay locked loop apparatus includes a first delay element to receive a reference signal, to delay the reference signal by a delay time, and to output a first delayed signal. A second delay element is used to receive the first delayed signal, to delay the first signal delayed signal by the delay time, and to output a second delayed signal. Also included is a harmonic lock prevention circuit to receive the reference signal, the first delayed signal, and the second delayed signal, and to adjust the delay time so that a period of each delayed signal is within a predetermined range.
1. A delay locked loop apparatus comprising:
a first delay element to receive a reference signal, to delay the reference signal by a delay time, and to output a first delayed signal;
a second delay element to receive the first delayed signal, to delay the first signal delayed signal by the delay time, and to output a second delayed signal; and
a harmonic lock prevention circuit to receive the reference signal, the first delayed signal, and the second delayed signal, and to adjust the delay time so that a period of each delayed signal is within a predetermined range.
2. The apparatus of claim 1 wherein the harmonic lock prevention circuit further comprises:
a first current steering phase detector to receive the reference signal and the first delayed signal and to output a signal based on a state of the first delayed signal;
a second current steering phase detector to receive the reference signal and the second delayed signal and to output a signal based on a state of the second delayed signal; and
a delay time adjustment circuit to increase the delay time if the state of the first delayed signal is high, to decrease the delay time if the state of the second delayed signal is low, and to output a harmonic lock prevent signal if the state of the first signal is low and the state of the second signal is high.
3. The apparatus of claim 1 wherein the delay locked loop further comprises a residual phase error correction circuit to receive the harmonic lock prevented signal and to correct a residual phase error in the delayed signals.
4. The apparatus of claim 1 wherein a boundary of the predetermined range is less than an integer multiple of a period of the reference signal.
5. The apparatus of claim 1 wherein the predetermined range of the period of each delayed signal has a first boundary that is greater than one-half the period of the reference signal and a second boundary that is less than three-halves the period of the reference signal.
6. The apparatus of claim 1 wherein the first delay element further comprises six transistors.
7. The apparatus of claim 2 wherein the a first current steering phase detector comprises an NMOS tree of XNOR gates.