JPS59189728A - Phase locked loop - Google Patents

Abstract

PURPOSE:To ignore the variation of an open loop gain to design a loop filter and obtain an excellent transient characteristic by not designing the loop filter in consideration of the variation of the open loop gain of a phase locked loop but adding a controller which makes the open loop gain constant. CONSTITUTION:A voltage corresponding to the phase between an input signal and a voltage control oscillator 3 is outputted by a phase comparator 1. This voltage is allowed to pass through a loop filter 2 to control the voltage control oscillator 3. The control voltage of the voltage control oscillator 3 is detected if the gain of the voltage control oscillator 3 is varied by an operating point, and a gain controller 6 controls the gain so that the open loop gain is constant.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a voltage controlled oscillator whose frequency changes depending on a control voltage, and a phase ratio generator which outputs a voltage according to a phase difference between an input signal and the output of the voltage controlled oscillator. The voltage controlled oscillator is connected to the phase comparator and the voltage controlled oscillator is connected to the voltage controlled oscillator.
A phase-locked loop consisting of a loop filter and a loop filter supplying the ll voltage.

First, a conventional phase-locked loop will be explained with reference to Fig. 2.1.

In FIG. 1, (1) is a phase comparator, (2) is a loop filter, and (3) is a sulfur pressure control oscillator.

Next, the operation will be explained.

The phase comparator (1) outputs a voltage according to the phase difference between the input signal and the output of the voltage controlled oscillator (3). By passing this voltage through a loop filter (2).

The voltage controlled oscillator (3) is split. or more phase synchronization rule
This is the principle behind the process.

In a phase-locked loop, the Seki loop transfer function is expressed as:

K+P(S) G(s)'' to ゛・Ks 8 Here, 1 is the sensitivity of the phase comparator (V/rad), K2 is the DC gain of the loop and filter, Ctf, )K3tJl is the sensitivity of the voltage controlled oscillator (rad/V ).When the ball rouge fn is represented by a Bode diagram, it becomes as shown in Figure 6.

In FIG. 6, (a)/fi is the gain, and (b) is the phase. If the phase-locked loop is optimally designed, the Bode plot will look like a solid line. At this time, the phase margin is φ. Now suppose that the open loop gain of the 9 phase locked loop has decreased by . At this time, the Bode diagram is.

It will look like a dashed line. At this time. The phase margin is zero, and the phase-locked loop causes unstable loop activation.

As described above, when the open-loop gain of the 9-phase locked loop decreases by more than a certain value, stable 0-phase locked loop oscillation occurs.

A possible cause of the decrease in the open loop gain of the phase-locked loop 9 is gain fluctuations of each component. General K
d, the gain variation of the voltage-controlled oscillator is the largest.

FIG. 2 shows an example of the voltage-frequency characteristics of a general voltage controlled oscillator.

The difference between the sensitivity (Δf/ΔV) at operating point 4 and the sensitivity (Δf/ΔV) at operating point 5 is obvious (6 dB in this example).The characteristics are phase and lock.

This is particularly noticeable in microwave band voltage controlled oscillators used in oscillators.

From the above, the phase-locked loop needs to be designed in consideration of fluctuations in the -loop gain.

For example, in the example shown in FIG. 6, it is necessary to design the loop gain at the minimum value of the sensitivity of the voltage controlled oscillator (3), but such a design will lead to deterioration of the transient characteristics.

This can be understood from the automatic control a theory.

In a conventional phase-locked loop, if the open loop gain fluctuates due to gain fluctuations of a voltage-controlled oscillator, the loop and filter must be designed to account for the fluctuation. Therefore, the transient characteristics deteriorate.

This invention was made to eliminate these drawbacks. In this invention, instead of designing the loop and filter by taking into account the fluctuations in the open loop gain of a single phase locked loop as in the past, the present invention adds a control device that keeps the open loop gain constant. It provides excellent phase locking looseness with transient characteristics by ignoring loop gain fluctuations.

This invention shown in FIG. 3 will be explained below.

In FIG. 3, (1) is a phase comparator, (2) is a loop filter, (3) is a voltage controlled oscillator, and (6) is a gain control device.

Next, the operation will be explained. The phase comparator (1) outputs a voltage according to the phase between the input signal and the voltage controlled oscillator (3). By passing this voltage through a loop and filter (2), a voltage controlled lifter (3) is controlled.

When the gain of the voltage controlled lifter (3) varies depending on the operating point, the gain control device (6) is configured to keep the open loop gain constant by detecting the control voltage of the voltage controlled lifter (3). ) controls the gain.

An example of a gain control device is shown.

The voltage-frequency characteristic of a voltage controlled oscillator generally approaches linearity as shown in FIG. The open loop gain is kept constant by correcting the gain with the gain control device (6) as shown in Figure 5 in response to the decrease in the gain of the voltage controlled oscillator. An example of the above circuit configuration is shown in an off-line diagram.

In the OFF diagram (71f81 is a hysteresis comparator, (9) is an operational amplifier 0QI (lltj switch).

Next, the operation will be explained. As shown in FIG. 4, it is assumed that the gain of the voltage controlled oscillator varies with the control @J voltages Vl and V2.

In the OFF diagram, when the control voltage of the voltage controlled oscillator is below Vl, the switch (In, switch α1) is ON. When the pressure becomes above v1, the hysteresis comparator (8) turns off the switch arp, and the gain of the DC amplifier is set to steresis. FIG. 5 shows that the comparator (7) turns off the switch θυ.

Note that various methods can be considered for the gain control device, such as a method using an analog circuit and a method using a digital circuit.

By using a digital circuit, it is easy to compensate for variations in open loop gain due to temperature as well as variations in open loop gain due to the operating point of the voltage controlled oscillator.

As described above, in the phase-locked loop according to the present invention, the open-loose gain is kept constant, instead of designing the loop filter taking into account the variation in the open-loop gain of the 0 phase-locked loop as in the conventional phase-locked loop. By adding a control device such as this, it is possible to design a loop filter while ignoring variations in the open loop gain, thereby providing a phase-locked loop with excellent transient characteristics.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining a conventional phase-locked loop. Figure 2 shows the voltage-frequency characteristics of the voltage controlled oscillator #5+
! FIG. 3 is a diagram explaining the phase-locked loop according to the present invention, and FIGS. 4, 5, and 5 are OFF diagrams. FIG. 6, which is a diagram illustrating an example of a gain control device, is a Bode diagram of a phase-locked loop. In the figure, +11 is the phase comparator, +211fi is the loop filter, (3) is the voltage controlled oscillator, (4) is the maximum gain operating point, (5) I/I minimum gain operating point, and (6) is the gain control device. , (71781 (81 is hysteresis comparator 19), +9) is an operational amplifier. (IQ+, (II) is a switch. Identical or corresponding parts in Figure 1 are indicated with the same symbols. Agent: Masuo Oiwa

Claims (1)

[Claims] a voltage controlled oscillator whose frequency varies depending on a control voltage;
a phase comparator that outputs a voltage according to a phase difference between an input signal and the output of the voltage controlled oscillator; and a loop filter that is connected to the phase comparator and supplies the control voltage to the voltage controlled oscillator. , and a gain control device that controls a loop gain according to the control voltage.