JPH03217124A - phase synchronized circuit - Google Patents

Abstract

PURPOSE:To quickly lock in an input signal by constituting a loop filter of a narrow band loop filter and a broad band loop filter and switching these loop filters and changing the characteristic of the broad band loop filter in accordance with the lock-in state. CONSTITUTION:When a certain lock-in state is attained within a time set by a filter control circuit 11, a filter control signal 12 does not change the characteristic of a broad band loop filter 2 to continue the lock-in operation. Otherwise, the filter control circuit 11 changes the characteristic of the filter 2 by the filter control signal 12. The characteristic of the filter 2 is so changed at this time that the input signal can be quickly locked in. Thus, the input signal which requires a long time for lock-in of cannot be locked in with the initial characteristic of the filter 2 is quickly locked in.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a phase-locked circuit, and particularly to a loop filter.

[Conventional technology] FIG. 2 is a block diagram showing a conventional phase synchronization circuit.

In the figure, 1 is a phase comparator that detects phase errors, 2 is a wideband loop filter, 3 is a narrowband loop filter, 4 is a voltage controlled oscillator, 5 is an input signal, 6 is an output signal, and 7 is a lock that detects phase lock. Detector, 8 is a filter switching signal for switching between the wideband loop filter 2 and the narrowband loop filter 3, 9 is a phase error signal, and 10 is an oscillation control signal.

In FIG. 2, a phase error is detected between an input signal 5 and an output signal 6, and a phase error signal 9 is output.

The phase error signal 9 is converted into an oscillation control signal 10 by the wideband loop filter 2 or the narrowband loop filter 3 by the filter switching signal 8 from the lock detector 7. The output signal 6 is input to the phase comparator 1, and this circuit is locked when the phases of the input signal 5 and the output signal 6 match.

Furthermore, immediately after the input signal 5 is input, it is asynchronous with the output signal 6 of the voltage controlled oscillator 4, which is oscillating at a free-running frequency, so the lock detector 7 detects the non-lock state and the switching signal 8 is transmitted over a wide band. Loop filter 2 is selected. Therefore, the voltage controlled oscillator 4 follows the input signal 5 and quickly becomes locked. When the locked state is reached, the lock detector 7 detects the locked state and switches to the narrowband loop filter 3 using the switching signal 8 so as not to follow the noise component contained in the input signal 4.

[Problems to be Solved by the Invention] By the way, in conventional phase-locked circuits, the band of the broadband loop filter is widened so that it can lock in quickly, so if there is a noise component in the signal in the lock-in region, the signal will track the noise component. If you do this, it may take a long time to lock in or you may not be able to lock in. Additionally, if lock-in takes a long time, the time it takes to switch from a wideband loop filter to a narrowband loop filter also becomes long. A wideband loop filter is used for the data region following the data signal, which may result in tracking noise components of the data signal or loss of lock.

SUMMARY OF THE INVENTION The present invention aims to solve these drawbacks, and its purpose is to provide a phase-locked circuit that can stably lock-in.

[Means for solving problem i1l] The phase locked circuit of the present invention inputs a detection result of detecting a phase error between an input signal and an output signal of a voltage controlled oscillator to a loop filter, and uses the loop filter to detect a phase error between an input signal and an output signal of a voltage controlled oscillator. In the phase-locked circuit configured to control oscillation of The present invention is characterized by comprising means for changing characteristics of the wideband loop filter.

[Example] Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows a phase locked circuit in one embodiment of the present invention. In the figure, the same parts as in FIG. 2 are given the same reference numerals. Further, 11 is a filter control circuit that monitors the lock-in state of the phase locked circuit and changes the characteristics of the broadband loop filter according to the state, and 12 is a filter control signal from the filter control circuit 11.

The filter control circuit 11 performs control to change the characteristics of the broadband loop filter using a filter control signal 12 if a certain lock-in state is not achieved within a set time.

Now, if a signal is input to the input signal 5, the input signal 5 and the output signal 6 which is oscillating at the free-running frequency are asynchronous, so the lock detector 7 detects an unlocked state and uses the filter control signal 12 to detect the non-lock state. Wideband loop filter 2 is selected, phase error signal 9 is converted into oscillation control signal 10 by wideband loop filter 2, and lock-in operation begins.

First, if a certain lock-in state is reached within the time set by the filter control circuit 11, the filter control signal 12 continues the lock-in operation without changing the characteristics of the broadband loop filter 2, and when the phases match, Lock detector 7
detects a locked state and switches to the narrow band loop filter 3 in response to a switching signal 8.

Next, if a certain synchronization state has not been reached within the time set by the filter control circuit 11, the filter control circuit 11
1 changes the characteristics of the broadband loop filter 2 using a filter control signal 12. If the characteristics of the wideband loop filter 2 after the change are changed to characteristics that lock in faster, input signals that would take a long time to lock in or could not be locked in with the initial characteristics of the wideband loop filter 2 can be changed. It is also possible to quickly lock in to

[Effect of the invention j As described above, according to the present invention, even when a signal that takes time to lock-in or cannot be locked-in is input, the characteristics of the wideband filter can be changed according to the lock-in state. This has the effect of quickly locking in by responding to the situation.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention. FIG. 2 is a circuit diagram of a conventional phase-locked circuit. 1... Phase comparator 2...Broadband loop filter 3...Narrow band loop filter 4...Voltage controlled oscillator 5...Input signal 6...Output signal 7...Lock detector 8...Filter switching signal 9...Phase error signal ・Oscillation control signal ・Filter control circuit ・Filter control signal

Claims (1)

[Claims] In a phase-locked circuit, the detection result of detecting a phase error between an input signal and an output signal of a voltage-controlled oscillator is input to a loop filter, and the loop filter controls oscillation of the voltage-controlled oscillator. It is composed of a narrowband loop filter and a wideband loop filter, and includes means for switching between the narrowband loop filter and the wideband loop filter, and means for changing the characteristics of the wideband loop filter depending on a lock-in state. phase-locked circuit.