JPH0278322A - Loop switching circuit for phase locked loop oscillator - Google Patents

Abstract

PURPOSE:To shorten loop locking time regardless of the limit of the power supply of a charge pump and of the supply capability by providing a switching circuit to a position where a capacitor and a resistor being components of a lag lead filter is short-circuited or opened. CONSTITUTION:The circuit consists of a digital phase comparator 2 detecting a phase difference of outputs between a reference oscillator 1 and a voltage controlled oscillator 4, a charge pump 3 converting the output into an analog voltage, resistors 7, 8 and a capacitor 9. Then an abnormal detection circuit 5 detecting the unlocked state of a loop is provided on a PLL circuit having the lag lead loop filter receiving an output of the charge pump 3 and outputting an APC voltage controlling the oscillated frequency of the oscillator 4. A switch 10 is arranged between the resistor 8 and the capacitor 9, disconnects the resistor 8 and the capacitor 9 in the case of the loop unlock by an output signal from the circuit 5 and short-circuits the resistor 8 and the capacitor 9 in the case of loop lock to switch the loop gain.

Description

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

[Prior Art] As shown in FIG. 2, a conventional loop switching circuit of this type includes a digital phase comparator 2 that detects the phase difference between the output of a reference oscillator l and the output of a voltage controlled oscillator 4, and a digital phase A charger voltage output 3 that converts the digital IB power of the comparator 2 into an analog voltage and outputs it, and a resistor 7. Resistance 8. It is used in a PLL circuit comprising a capacitor 9 and having a lag-lead loop filter that inputs an analog voltage output from a charge pump 3 and outputs an APC voltage for controlling the oscillation frequency of a voltage controlled oscillator 4. Ta. An abnormality detection circuit 5 uses the output of the digital phase comparator 2 to detect the unlocked state of the loop, and an output control signal from this abnormality detection circuit 5 shorts both ends of the resistor 8 when the loop is unlocked. When the loop is locked, the analog switch 6 is connected in parallel to the resistor 8 so that both ends of the resistor 8 are open to switch the loop gain.

When the loop is unlocked by this switching circuit, the analog switch 6 described above is short-circuited, and the loop gain increases, making it possible to quickly reach the desired frequency.
It is A.

[Problems to be Solved] In the conventional loop switching circuit described above, even when the loop is unlocked and both ends of the resistor 8 are shorted by the analog switch 6, the capacitor 9 is connected to the charge pump 3. Here, the ability of the charge pump 3 to charge the capacitor 9 is determined by the power supply capacity of the charge pump 3, and the power supply capacity of the charge pump 3 has a limit. Therefore, there is a limit to the ability to charge the capacitor 9, and this limit loop pull-in time is lengthened.

Further, when the loop gain needs to be lowered when the loop is locked, the capacitance of the capacitor 9 becomes particularly large, which causes the problem that the above-mentioned drawback becomes more pronounced.

The present invention has been made in view of the above-mentioned problems.
By providing a switching circuit in a position where the capacitor and resistor that make up the lag lead filter can be short-circuited or opened, it is possible to shorten the loop pull-in time regardless of the limit of the charge pump's power supply capacity. The purpose of the present invention is to provide a loop switching circuit for a phase-locked oscillator.

[Means for Solving the Problems] In order to achieve the above object, a loop switching circuit for a phase-locked oscillator according to the present invention includes a phase comparator that receives the output of a reference oscillator and the output of a voltage-controlled oscillator, and In a phase-locked oscillator circuit that includes a charge pump that receives an output signal as an input, and a lag-lead loop filter that receives the output signal of the charge pump as an input and outputs an APC voltage for controlling the oscillation frequency of the voltage-controlled oscillator, The configuration is characterized in that a switching circuit is provided at a position where a short circuit or an open circuit can occur between the resistor and the capacitor of the lag lead type loop filter.

[Example] Five examples of the present invention will be described below with reference to FIG. In addition, common reference numerals are given to parts that are common to the conventional art and will be explained.

FIG. 1 is a block diagram of one embodiment of the present invention.

The illustrated circuit includes a digital phase comparator 2 that detects the phase difference between the output of the reference oscillator l and the output of the voltage controlled oscillator 4;
A charge pump 3 converts the digital output of the digital phase comparator 2 into an analog voltage and outputs it, and a resistor 7. Resistance 8. The analog voltage output from the charge pump 3 is input to the capacitor 9 and is used to control the oscillation frequency of the voltage controlled oscillation gA4.
The abnormality detection circuit 5g4 is a PLL circuit having a lag lead type loop filter that outputs an rc voltage, and uses the output of the digital phase comparator 2 to detect the unlocked state of the loop.

The analog switch IO is arranged between the resistor 8 and the capacitor 9, and in response to the output control signal from the abnormality detection circuit 5, opens the resistor 8 and the capacitor 9 when the loop is unlocked, and opens the resistor 8 and the capacitor 9 when the loop is locked. The capacitors 9 are connected so as to be short-circuited, and the loop gain is switched.

[Effects of the Invention] As explained above, the present invention provides power supply to a charge pump by providing a switching circuit at a position where a short circuit between a capacitor and a resistor that constitutes a lagged-lead loop filter of a PLL circuit can be released. Regardless of your ability, increase the loop gain sufficiently.

This has the effect of shortening the pull-in time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the present invention, and FIG. 2 is a block diagram of a conventional loop switching circuit. l: Reference oscillator 2: Digital phase comparator 3: Charge pump 4: Voltage controlled oscillator 5: Abnormality detection circuit 7: Resistor 8: Resistor 9: Capacitor 10: Analog switch

Claims (1)

[Claims] a phase comparator that receives the output of the reference oscillator and the output of the voltage-controlled oscillator; a charge pump that receives the output signal of this phase comparator; In a phase-locked oscillator circuit having a lag-lead loop filter that outputs an APC voltage for frequency control, a switching circuit is provided at a position where a resistor and a capacitor of the lag-lead loop filter can be short-circuited or opened. Features a phase-locked oscillator loop switching circuit.