DE1214721B - Automatic frequency control circuit - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

H04n

German KL: 21 al -35/12

Number: 1214 721

File number: F 27821 VIII a / 21 al

Filing date: February 28, 1959

Opening day: April 21, 1966

The invention relates to an automatic frequency control circuit for frequency equalization using a pulse train supplied by a generator with a reference pulse train a circuit in which a signal is generated that identifies the source that has the higher number of pulses generated, and with the difference frequency of the pulse series, a counter is actuated by the identification signal is controlled and a control voltage is generated, which is determined by the difference between the reference pulse number and generator pulse number and the phase difference between the fundamental frequency components of the two pulse series as well as on the direction of this difference and is fed to the generator for regulation.

It is known, the generator oscillation and the reference oscillation of a phase comparison circuit to supply the one of the phase difference between the two oscillations dependent control voltage generated, whereby this control voltage is used to readjust the frequency of the generator. In the television sync generation example, this vibration generator is common a control oscillator which generates an oscillation of a suitable multiple of the line frequency. The oscillation is applied to a divider chain, which results in an oscillation with the frequency of the image change generated by a phase comparison circuit for comparison with a reference oscillation is fed. Since it is often necessary to give the frequency control circuit a large time constant give in order to prevent undesired rapid frequency changes of the control oscillator, results the difficulty that the generator is not fast enough in terms of its frequency with the reference frequency can come into harmony if the frequency of the control oscillator is not already very close to Setpoint is.

It is also already known to have a first counter to be acted upon by the reference frequency and a second counter of the generator frequency to be regulated, the two counting results of the counters being compared with one another after a certain time and from this a voltage for influencing and readjusting the generator is derived will. However, this circuit has the disadvantage that it is necessary to readjust the generator Voltage only occurs when the counting results of the two counters differ by a certain amount differ. This fact leads to the great disadvantage that the generator frequency never exactly in accordance with the target frequency - Automatic frequency control circuit

Applicant:

Ferguson Radio Corporation Limited, London

Representative:

Dr.-Ing. E. Liebau, patent attorney,

Göggingen via Augsburg, v.-Eichendorff-Str. 10

Named as inventor:

Felix Rozner, Kenton, Middlesex;

Francis Oakes,

John Victor James Corney, London

(Great Britain)

Claimed priority:

Great Britain from February 28, 1958 (6600) - -

can be brought, but that there is always a certain difference frequency left over.

After all, attempts have already been made to reduce the generator frequency to a certain Value to regulate that one by means of a rotating contactor for a certain time the impulses of the Generators of a counting chain and the readjustment of the generator from the result of this Counting makes you dependent. The disadvantage here, however, is that an electric motor for influencing the Generator is required, and further that it is difficult to reach the rotating contactor To let work with always the same speed, and also in such a way that really the counting chain is only connected to the generator for a precisely defined period of time.

Furthermore, an automatic frequency control circuit has already become known in which by means of of a relay, a resistor influencing the time constant of the control system can be short-circuited can. The voltage to operate the relay is supplied by a discriminator that determines the frequency compares the generator to be controlled with the setpoint frequency. In this way it should be achieved that 'The control circuit initially has the option of setting the frequency relatively quickly when the time constant is large of the generator to be controlled to adapt to the setpoint frequency, after which, if the output

609 559/288

3 4

output voltage of the discriminator to a small time as a Rozner phase comparison circuit

constant is reversed by the relay, where, together with the associated gate circuits,

a curve to explain the effect by matching FIG. 4 as closely as possible

Frequencies to be compared with one another are achieved by the phase comparison circuit according to FIG. 3,

shall be. However, this known circuit has 5 F i g. 5 is a circuit diagram of the first counter stage in

the following disadvantages. It happens that after time F i g. 2 with the associated goals,

occasional disturbance of the reception the frequency of the waveforms shown in FIG. 6 at different points

in the meantime, those who continue to work on their own in FIG. 2, 3 and 5 and

The resonant circuit is no longer at the setpoint frequency. Fig. 7 and 8 curves to explain the effects

exactly matches. In order now to synchronize again from FIG. 2.

The meaning of the lettering in different constant means of the relay is required, there being blocks in FIG. 2 is indicated below the figure. the it takes a certain time for the setpoint frequency to approximate again at various points in FIGS. 2, 5 and 7 is reached and finally after re-emerging waveforms are shown in these figures Switching to large time constant the exact 15 of the letters indicated that these waveforms Adjustment has been made. The various toggle in FIG. 8 denote.

operations lead when used in television receivers In Fig. 1 it is assumed that the frequency is a

like to picture disturbances that last for a certain time. vibration generated by a control oscillator 10

Finally, one already has a frequency-dependent control circuit supplied at 11 A frequency oscillation is to be controlled in parallel to one another. When the loading and a phase comparison is carried out. This is the appropriate frequency for a satisfactory regime However, if the frequency of a generator is not too high, it will be increased by a frequency one Target frequency adjusted exactly, but divider 12 is reduced to a lower value. the aspired to the frequency of the oscillating oscillations to be controlled by 12 and 11 are a counter tor at a certain distance from the target 25 13 supplied, which is switched so that it the differential frequency to keep. Otherwise it is a matter of the difference between the number of periods of the two a circuit that counts vibrations applied to a multi-channel telephone system. The vibrations with suppressed carrier is suitable, in which of 12 and 11 also become phase degradation Reference frequency is supplied to a separately received pilot equalization circuit 14, which is connected in such a way that frequency of comparatively high oscillation 30 that it generates a voltage at 15 that is from the prefix is. sign of the frequency difference depends, and this

To avoid these disadvantages, according to the voltage, an addition-subtraction switch

Invention, a phase comparison circuit upstream 16 is supplied, which is coupled to the counter 13

see which is one of the direction of the phase difference. The effect of this tension is the

dependent directional control voltage generated and to cause 35 counter that he

whose output control voltage generated in this way with a gate circuit 17 at each count

is bound that the control voltage in each case at least according to the sign of the frequency difference

controls one of several gates that are enlarged or reduced between generator. The control voltage

or reference pulse source and counter is switched on via a low-pass filter 18 of a variable response

are and the pulse difference of the respective Im- 4 ° 19 supplied, which is used to control the frequency of the

Pulse source higher number of pulses to the input of the control oscillator 10 is used.

Let the counter pass, with the counter at its If necessary, a frequency control switch output can be used under control by the directional control tang of known design in addition to the clothing a series of positive or negative span letters can be provided. Then generates the voltage values are generated and the voltage from the 45 phase comparison circuit 14 at its output 20 Counter output to the generator to control a voltage, the size and direction of which depends on the to be led. This achieves the advantage of the size and sign of the phase difference that the control circuit is on the one hand with a high accuracy between the input values of 12 and 11 works by requiring a phase comparison. This tension is in a mixer see the two voltages carried out, 50 21 mixed with the control voltage of 17, and the but on the other hand, even with a larger frequency, the combined control voltage becomes the low-pass filter frequency deviations' only elapsed for a short time, 18 added.

until synchronization is restored because the circuit shown in FIG. 2 is used when

Circuit works continuously with a small time constant. Television for generating line and picture

In one embodiment, the invention is 55 frequency pulses, which are determined by a reference frequency, explained in more detail with reference to drawings, for example from the power supply network, shows will hold. A sinusoidal reference frequency

Fig. 1 is a simplified block diagram of a is fed to the terminal 25 and comes from Embodiment of the invention, in which both one here one after the other via an integrated separation stage 26, voltage derived from a slip counter as 60 a square-wave converter or amplitude limiter also one derived from a phase comparison circuit 27 and a differentiating separator 28 on its lead-out Voltage used for frequency control gear generates a series of reference pulses as shown in Fig. 6, (α). In Fig. 6

FIG. 2 is a detailed block diagram of FIG. ¹ showing waveforms (b), (c), (d) and (e) den

Leadership according toFig. 1, 65 case where the frame rate is greater than the reference

F i g. 3 is a circuit diagram of a preferred execution frequency and waveforms (/), (g), Qi) and

Approximate form of a phase comparison circuit for the (7) represent the case in which the frame rate

Turn in the circuits according to Fi g. 1 and 2, which is less than the reference frequency.

5 6 '

A control oscillator Qr 10 generates oscillations from the reference frequency close to the limits of the

double line frequency, and its Äusgangsspan- working range is. If the attenuation of the

tion is correctly dimensioned via a separation stage 29 of a first Aus system, these goals are from

input terminal 30 supplied. This clamp is of lesser importance.

a divider 12, which divides by 405, with a second 5 The voltage on line 35 can only be one

Output terminal 31 connected, which assume the image-limited number of fixed values, as in

frequency output forms. The frame rate becomes Fig. 7, (d) shown, and that described above

a differentiating separation stage 32 out, the image system must consequently between the two fre-

frequency pulses generated as they oscillate back and forth in Fig. 6 at (b) sequences, the two of these

or (/) are shown. io values on both sides correspond to the reference frequency.

The reference pulses and the frame sync pulses Since the in F i g. 3 shown Rozner phase comparison

of 28 or 32 are a Rozner phase connection over a total range of 2 π im

DC circuit 14 supplied. The exit at B radians works (F i g. 4) and one step of the trep-

from waveform (c) goes ap. a line 33 and pen-shaped voltage of a period of the difference

from here on a series of coincidence _{gates Cr 12} , 15 corresponds to a pulse train, the output of the

G ₂₂ , G ₃₂ . . . G ₀₂ . The other output of the phase-matching circuit to fill in the gaps in the

comparison circuit 14 at A of the waveform, (g) rich 4 ^it counter can be used. This is done in

goes to a line 34 and from here to a series F i g. 2 reached by the resistance R _f , which is in the

of coincidence gates G ₁₁ . . . G ₆₁ . The gate G ₁₂ is input a voltage shown in Fig. 7, (b)

with frame rate pulses (b) or (/) of 32 and 20, which is the average collector potential in the

represents the gate G ₁₁ with reference frequency pulses (α) from 28 phase comparison. The result

fed. The output of the gates G ₁₁ and G ₁₂ goes to the addition of this interpolation voltage to the

the first counter B _{1 is} one of six binary counting stair-shaped voltages in FIG. 7, (c) shown

levels B ₁ to B ₆ existing binary counting chain. This represents. The interpolation voltage corresponds to

Counters will be explained in more detail later with reference to FIG. 5. The voltage shown in FIG

purifies. Their outputs are routed through separate back mixers 21:

R stands out _xt ... R _{x 6} to a line 35, on when the Interpolationsspannung is low at which creates a voltage on the number of as shown in Fig. 8, (a), the result is an unstable counted pifferenzimpulse and from the relative range as shown in FIG. 8, (c) is shown, over which the phase position between the image and reference pulses 30 system oscillates. It depends on that to avoid this. Resistance R _{t is given} a slightly smaller value than the voltages (g) and (c) on lines 34 is required to achieve a maximum current equal to that and 33 open the associated gates when they achieve positive current from that to which Counter B are ₁ . Thus, when the reference frequency is obtained the associated resistance R _xt . The higher is, the waveform (g) on the line 34 35 follows is a slight overlap as shown in the illustration, the gate G ₁₁ opening and the passage of the impulse in FIG. 8, (b), the control according to FIG. Allow pulse {h) to counter B ₁ . The goals (d) result. Within the overlap area there are G ₂₁ . . . G ₀₁ are actuated simultaneously, and a two stable phase relationships "exist, which can generate a staircase voltage (/) appears on the line 35. The given control oscillator frequency to the variable reactance 19 to subtract the waveform (g), which readjusts the frequency of the control oscillator 10. Resistor R / and a capacitor C reached B of the phase frequency of the control oscillator is increased.Circuit circuit 14 connected to an alternate-If the frame rate is higher than the reference 45 native solution to the low-pass filter 18 in FIG an alternating current component in the form (c) on the line 33 the gate G ₁₂ to the antiphase to that of the output A via the cons-difference pulses (d) _{to let} through, and makes stand R f and keeps the latter in equilibrium without also gates G ₂₂ . . . G ₀₂ permeable. The change in the constant mean direct current, staircase-shaped signal on the line 35. then has 50 The curve shape (e) caused by the interpolation voltage circuit, and its effect consists in the time delay caused by a time that it compensates for the frequency of the control oscillator 10 delay, which diminishes in the stair span. circuit through a time delay network To prevent the 39 from being inserted in the event of a suspension. This time delay should not be longer than the reference frequency, the frame frequency regulated towards zero, than is necessary in order to use an oscillation, as the system would do if the output is to be avoided. A value of about 0.2 seconds appears from 27 via a detector 38 to the gate G ₁₂ - sufficient in the present example in which it is coupled. This has the effect that when R / and C are interrupted, a time constant of 0.5 seconds at the input of 38, the gate G ₁₂ remains closed.

and the passage of further image pulses to the counter 60 In Fig. 3 the circuit of the Rozner phase

ler B ₁ prevented. As a result, the frequency comparison circuit 14 and the gates G ₁₁ and G _{12 change}

sequence of the control oscillator 10 only slightly compared to FIG. 2 shown. For the diodes D ₁ and D _{2 of} the

their value immediately before the gates are released are the type OA 79 and for all others

Reference oscillation. Diodes in FIG. 3 the type OA 70 is used.

The gates G ₇ and G ₈ set the counter at the end 65 The Rozner phase comparison circuit also works

silent in order to prevent that due to a missing trailing edge of the image and reference pulses .. On

counting or a dynamic overshoot pulse of both types puts the comparator in one

passes directly from one end to the other if state in which a) a following pulse if he

comes from the same source (picture or reference), through gate G ₁₁ or gate G ₁₂ , and b) the gates coupling the counter stages are set so that they cause an analog change in the correct sense. The setting impulses do not get into the counter themselves. If the frequencies are the same, the following pulse is inevitably of a dissimilar nature and sets the gates coupling the counters to zero for themselves. Only if the frequencies are different can two effective edges of the higher-frequency pulse series occur between two effective edges of the low-frequency pulse series, as shown in FIG. 6, (α) and (b) , and this condition occurs once per period of the differential pulse train. The second pulse of the same type is then let through into the counter and counted with in the corresponding sense.

FIG. 5 shows the circuit of the first binary counter B ₁ with the ports G ₂₁ and G ₂₂ of FIG. 2. The diodes D ₃ and D ₁ are of the type OA 79, and all other diodes are of the type OA 70.

The resistors R _xl to R _{x 6} in FIG. 2 have values of 1500, 820, 400, 200, 100 and 50 kilohms in the order given.

The count chain in the circuit of Fig. 2 stores a total count of (2 ^6-1 ) periods and the range of the analog output is thus 64 periods. This controls the frame rate from 47 to 52 Hz, and the time constant of the control loop is ⁶ Vs seconds, ie approximately 12 seconds. This not only achieves a large holding area, but also an advantageously long time constant.

While the invention is illustrated specifically as applied to television signals, it is not limited to this, rather it can be used wherever a generator of an oscillation or be kept in step with a reference oscillation or a series of impulses by impulses target.

Claims (3)

Patent claims: 1. Automatic frequency control circuit for keeping the frequency of a pulse train supplied by a generator equal to a reference pulse train, using a circuit in which a signal is generated which identifies the source which generates the higher number of pulses and a counter is operated with the differential frequency of the pulse trains, which is controlled by the identification signal and generates a control voltage which depends on the difference between the reference pulse number and generator pulse number and on the phase difference between the fundamental frequency components of the two pulse trains and on the direction of this difference and is fed to the generator for regulation, characterized in that a phase comparison circuit (14) is provided, which generates a directional control voltage dependent on the direction of the phase difference and whose output (A, B) is connected to a gate circuit in such a way that the control voltage is at least one of several gates (G ₁₁ or G ₁₂ ) controls, which are switched on between generator (10) or reference pulse source (25) and counter (B ₁ ) and pass the pulse difference from the respective pulse source higher pulse number to the input of the counter (B ₁ ) , and that -the counter at its Output (35) generated a series of positive or negative voltage values under control by the directional control voltage and the voltage from the counter output (35) is fed to the generator (10) for regulation. 2. A circuit according to claim 1, characterized in that the counter is formed by a binary counting chain (B ₁ ... B ₆ ) , in which the inputs to each counting stage through two gates (G ₁₁ ... G ₀₁ or G ₁₂ ... G ₆₂ ) and all gates are controlled by the voltages from the starting points (A, B) of the phase comparison voltage. 3. A circuit according to claim 1 or 2, characterized in that a circuit part (R _f , R /, C) is provided through which an interpolation voltage is combined with the voltage at the output (35), which is taken from the phase comparison circuit (14) will. Considered publications:
German Patent No. 1001343;
U.S. Patents Nos. 2,490,499, 2,490,500,
2610297; British Patent No. 637 380. For this purpose 2 sheets of drawings 609 559/288 4.66 © Bundesdruckerei Berlin