PLL LOCK DETECTION CIRCUIT AND SEMICONDUCTOR DEVICE
A PLL lock detection circuit produces a high precision PLL lock detection signal and enables eliminating a smoothing circuit. The PLL lock detection circuit reliably detects if the PLL circuit is locked reliably and without error by simultaneously evaluating both locked and unlocked states. A continuity detection unit detects if a PLL locked state continues for H consecutive periods, and another continuity detection unit detects if a PLL unlocked state continues for H consecutive periods. The continuity detection units simultaneously output the PLL locked/unlocked states, and an R-S latch holds the detection result.
1 . A PLL lock detection circuit operable to detect the phase state of a PLL circuit that generates a signal synchronized to the phase of a reference signal that has a pulse of a predetermined period and a variable logic level, comprising:
a phase comparison unit that compares the reference signal and a comparison signal, and generates a comparison result signal;
a smoothing unit that levels the comparison result signal and generates a smoothed signal;
an oscillation unit that generates a comparison signal with a period substantially equal to the predetermined period based on the amplitude of the smoothed signal; and
a phase state detection unit that detects a phase state and generates a phase state signal based on a logic level of the reference signal or the comparison signal at a specified point in the period of the other of the reference signal and the comparison signal.
2 . The PLL lock detection circuit described in claim 1 , wherein said phase state detection unit generates the phase state signal when a phase state in which the logic level at the prescribed point in the period is the same level for N consecutive periods (where N is an integer of 2 or more).
3 . The PLL lock detection circuit described in claim 2 , wherein said phase state detection unit comprises:
a locked state detection unit that determines the phase state is the locked state when the logic level is a first level;
an unlocked state detection unit that determines the phase state is the unlocked state when the logic level is a second level; and
a phase state signal generating unit generates a phase state signal denoting the state between when the locked state is detected and when the unlocked state is detected.
4 . The PLL lock detection circuit described in claim 2 , further comprising:
a continuity count setting unit that sets the continuous count N and generates a continuity count signal;
wherein said phase state detection unit generates the phase state signal based on the continuity count signal.
5 . The PLL lock detection circuit described in claim 2 , further comprising:
a predetermined period signal generating unit that generates a predetermined period signal denoting the predetermined period; and
said phase state detection unit holds the logic level of the phase state signal for the predetermined period based on the predetermined period signal.
6 . The PLL lock detection circuit described in claim 1 , wherein said phase state detection unit generates the phase state signal based on the logic level of the reference signal at an edge of the comparison signal.
7 . The PLL lock detection circuit described in claim 1 , wherein said phase state detection unit generates the phase state signal based on the logic level of the comparison signal at an edge of the reference signal.
8 . The PLL lock detection circuit described in claim 7 , wherein:
said phase state detection unit comprises a duty factor changing unit that changes the duty factor of the comparison signal and generates a changed comparison signal, and
generates a phase state signal based on the logic level of the changed comparison signal.
9 . A semiconductor device composed of a single semiconductor chip that is used in a PLL lock detection circuit operable to detect the phase state of a PLL circuit that generates a signal synchronized to the phase of a reference signal that has a predetermined period and a variable logic level, the PLL lock detection circuit including a phase comparison unit that compares the reference signal and a comparison signal, and generates a comparison result signal, a smoothing unit that levels the comparison result signal and generates a smoothed signal, an oscillation unit that generates a comparison signal with a period substantially equal to the predetermined period based on the amplitude of the smoothed signal, and a phase state detection unit that detects a phase state and generates a phase state signal based on a logic level of the reference signal or the comparison signal at a prescribed point in the period of the other of the reference signal and the comparison signal, the semiconductor device comprising:
said phase state detection unit.
10 . The semiconductor device described in claim 9 , further comprising:
said phase comparison unit;
said smoothing unit; and
said oscillation unit.