DE1939436A1 - Overlay receiver with automatic frequency control - Google Patents

Description

Dipl.-Ing. ERICHE. WALTHEß 'phn., Ρ.'π ₇ ,

Patent attorney JW / VJM ..

Applicant: N.V. PHILIPS 'GL0EILAMPENFA8J? Lf «£

Act., PM- 3417
dated »1, Aug. 1969

Overlay receiver with automatic frequency control ".

The invention relates to an overlay receiver with automatic frequency control for receiving electrical transmitter signals, which has a tunable overlay oscillator for generating a local oscillator oscillation, a mixer for mixing the received signals with the local oscillator oscillation, an intermediate frequency amplifier for amplifying the output signal of the Mixing stage, which intermediate frequency amplifier is provided with one or more blocking circuits to suppress signals from a transmitter that is adjacent in its frequency _t a frequency discriminator tuned to the desired intermediate frequency, to which the signal of the intermediate.

PIlN. 3 ^ 17 * - 2 -

frequehzvers booster is fed, and one of a fixed Reference voltage; provides opposite rule voltage, the parallel capacitor used to smooth the control voltage to control the frequency of the local oscillator oscillation fed to the local oscillator becomes, as well as means for switching the frequency of the local oscillator vibration for the transition from receiving a Transmitter signal to the reception of another transmitter signal

^ erithäl t.

In such receivers, automatic frequency control of the superimposed oscillator is used to achieve greater accuracy in the tuning of the receiver, in spite of regularly significant tolerance errors, temperature drift, supply voltage injection and aging of the frequency-determining elements of the superimposed oscillator. All of these causes of error are further referred to as "tolerance errors". The detuning caused by this tolerance error also causes the frequency discriminator to detune the supplied intermediate frequency signal with respect to the correct intermediate frequency, and through this detuning, the frequency discriminator supplies a cone voltage that differs from the reference voltage, with the help of which the frequency of the local oscillator oscillation is shifted in the same way that the resulting detuning is reduced.

However, it has been found that the receivers described above when switching from reception

PHN. 3kIJ.

of the one transmitter signal to the reception of another transmitter signal the automatic frequency control in some cases is ineffective, at least is unable to set the frequency of the local oscillator down to about the correct one for optimal reception desired value shift.

The invention aims at., To provide a superheterodyne receiver of the above kind in which a maximum effect is ensured of the automatic frequency control under all · circumstances, and the inventive circuit arrangement has to d & t is characterized in that further switching means are connected to said parallel capacitor, with coupled to said means for switching the frequency of the local oscillator oscillation and which apply said control voltage for regulating the frequency of the local oscillator oscillation to the fixed reference voltage during this switchover.

The invention is based on the following knowledge. It is assumed that the tolerance error « of the elements that determine the frequency of the local oscillator vibration are dimensioned such that a certain maximum detuning ^ f. versus the right one

ΙΠ ei X

Tuning frequency of this oscillation is not exceeded. This upset can be both positive and negative.

Assume that the receiver is tuned to a transmitter signal, with the tolerance error in the local oscillator causes a detuning ^ f in a positive direction. The circuit arrangement for the automatic fre-

009808/1235

BAO

PHN. 3 ^ 17

In this way, speed control delivers the local oscillator a lying] voltage which roughly corresponds to the value wf

m a χ

causes rapid frequency advance in the negative direction, so that this makes the local oscillator approximately is tuned to the correct frequency

, It is further assumed that the recipient is on ile reception of a different transmitter signal is switched, where the tolerance error in the local oscillator is a

* Cause detuning ^ f in the negative direction. Infol-

nifi χ

ge of Paral1 el cond "nsators which is used to smooth the control voltage, the Hegel voltage for a short time original on (Jem are retained Who * L, where the vibration generated by I'bor 1 agerungsoszil la tor another zusätzliehe frequency shift ^ f experiences in the negative direction and the total frequency shift therefore corresponds to twice the value 2 Δ 1 'in the negative direction, max ^u .

One that big «? Detuning of the superimposition

k 7i 1 lalors has tneis-

This means that the frequency of the desired intermediate frequency signal lies beyond the oscillation frequency of the trap circuit, which is provided in the intermediate frequency amplifier, in order to suppress the reception from neighboring specials capable of 'a Proquenzkorrek t ur carried out, in which the frequency of the desired signal exceeds the Sdiwjngurigsfrpquenz of the prohibited area, because, even where η η di ο frequency <leo gewünschtan Si gna Js of vibration

009808/1235

PHN. 3417

frequency of the trap circuit corresponds to the frequency discriminator no signal is supplied, and this discriminator consequently does not supply any control voltage. The signal you want therefore remains in front of the oscillation frequency of the trap circuit and the receiver therefore does not stand on the correct tuning.

The measure according to the invention

is enough that after each switchover from receiving a transmitter to another transmitter the parallel capacitor for smoothing usually voltage is applied to the reference voltage, so that the automatic frequency control always after each channel switching starts from this reference voltage. The upset of the local oscillator can therefore never "higher than the maximum due to the tolerances of the frequency determining elements of the local oscillator caused detuning Δ f. By having these tolerances

^to max '

be chosen such that the frequency of the intermediate frequency signal rjicht beyond the oscillation frequency of the is located in the intermediate frequency amplifier trap circuit for suppressing signals from neighboring transmitters a correct effect of the circuit arrangement for the automatic frequency control is always guaranteed.

Embodiments of the invention are shown in Drawings shown and are described in more detail below. Show it

Fig, T a receiver according to the invention Reception of television signals,

009808/1235 bath

PHN. 3'H7. - 6 -

2 shows a characteristic curve to explain the mode of operation of the receiver according to Fig. 1,

Fig. 3 pin according to the invention receiver for Reception of color television signals,

Fig. H shows an embodiment of a switching arrangement for use in a receiver according to the invention,

F ¹ Jg. 3 shows a detailed circuit for use in a receiver according to the invention.

Fig. 1 shows a television receiver in which

the signals to be received are fed to a channel selector .2 with the aid of an antenna 1. This channel selector contains a mostly tunable preamplifier tufo 3, a superposition oscillator k and a mixer stage 5 »to which the signals of the preamplifier stage 3 and the oscillation generated by the local oscillator are fed. The output signal of the mixer 5 is fed to an intermediate frequency amplifier b.

The intermediate-frequency holiday signal amplified by this amplifier contains, if correctly tuned, a main carrier on, for example, 3 ^, 9 spleen, on which the video signal is modulated, and a sound carrier on 33 '' + MIIz, on which the audio signal is modulated. A conventional amplitude frequency transmission curve of the intermediate frequency amplifier 6 is shown in FIG. This transmission curve contains an inclined part, the so-called Nyquist FJanke, near the 3 ^ ^: » 9 MHz main carrier and a lower one

009808 / 123S

- BAD ORiGiNAL

• ■. PHN. 3 ** 17

lying part to the passage of the sound carrier of 33.4 MHz modulated sound signal.

The intermediate frequency amplifier 6 contains blocking circuits, shown schematically in FIG. 1, for suppressing the main carrier of the one and the sound carrier of the other television channel which is adjacent in frequency. If the channel spacing is 7 MHz, these carriers are at 31 ι ^q or ho, U MHz. As a result of these trap circuits, the transmission curve of the intermediate frequency amplifier 6 shown in FIG. 2 contains sharp curve breaks at 31 19 and ho _t k MHz.

The output signal of the intermediate frequency amplifier b is fed to a video demodulator 7t, which is used to generate the demodulated picture signal. This picture signal is fed to a display device (not shown ). Subcarrier and the 3 *, ^q MHz main carrier a 5.5 MHz subcarrier to which the audio signal is modulated. This intermediate carrier signal is fed to a tone demodulator 9 via a pin subcarrier amplifier f *, from which demodulator the low-frequency tone signal is fed to a display device not shown in detail.

For the automatic frequency control of the superimposing oscillator k , the receiver according to FIG. 1 contains a frequency discriminator 10 to which the signal amplified in the intermediate frequency amplifier (ι is fed and which is tuned ^{to the desired carrier frequency of 3 | S} ι ^{() MHz.}

009808/1235

original

PHN. 3 ^ 17

This Froqupnzdiskriminator supplies the oscillator h via a parallel smoothing correlator 11 with a control voltage that is positive or negative with respect to a host i min th reference voltage (in this case the mass polarity), depending on whether the carrier frequency of the signal fed to the frequency discriminator is higher or higher. is lower than the 3d., 9 MHz frequency to which dip the discriminator is tuned. For example, if the frequency of the local OszJ1latorschwingung% to 1 MHz is high, the carrier of the intermediate frequency signal is also about 1 MHz to up to 39 »9 MHz. This carrier causes, for example, a positive cone voltage at the output of the frequency / discriminator 10, and with the help of this positive cone voltage, the frequency of the superimposition oscillator is lowered by 0.9 MHz, for example, so that the last I0n.des only detuning of "0 , 1 MHz occurs. If the local oscillator frequency becomes too low, the frequency detector generates a negative voltage in the same way, which increases the local oscillator frequency.

frequency brings about.

To switch the receiver from one television channel to the other, the receiver contains a mechanical channel switching device, symbolically represented by button 12. With this channel switching device, the frequency-determining elements of the ns / i1 a tor and mostly also the tuning elements of the foreman are changed in a manner known per se.

As described at the beginning, it can happen that

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BATH

PHN. 3 ^j * 1 7
- 9 -

such a large detuning of the
Local oscillator that this detuning occurs
can no longer be corrected by the automatic frequency control. If, for example, the local oscillator in the new position of itself delivers a frequency 1 MIIz too high, and if the capacitor 11 continues
supplies a control voltage originating from the previous position, which also causes the local oscillator frequency to increase by 1 MHz, the overall detuning of the local oscillator is 2 MHz. The intermediate frequency carrier is then at h 0.9 MHz and this detuning can
no longer readjust themselves by means of automatic frequency control, since the blocking circle frequency of hO, h MHz has to be passed.

To avoid this disadvantage, the capacitor 11, a switch 13 is connected in parallel with the
Channel switching device 12 is coupled. Is in normal operation. the switch 13 is open; When the channel is switched, the switch 13 is closed for a period of time, whereby the capacitor 11 is discharged to approximately the reference voltage (ground potential). In this way it is achieved that the control voltage of the automatic frequency control always starts after each channel switch from the reference voltage and the above-described accumulation of detunings of the local oscillator is therefore avoided,

3 shows a color television receiver according to the invention. In this figure with the same reference numbers

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BATH ORIGINAL

PHN. 3h 17.

- 10 -

elements as indicated in FIG. 1 have the same task > and therefore do not require any further explanation. That from Intermediate frequency amplifier 6 supplied intermediate frequency signal In addition to the carrier shown in FIG. 2, contains 38.9 MHz and sound carriers of 33.1 MHz still ο inen suppressed Carrier of 3 ^, 5 MIIz on which the color information is modulated is.

The output signal of the intermediate frequency amplifier 6 is on the one hand fed to the demodulator stage 7, in which the 5.3 MHz intermediate carrier is formed from the mixture of the sound carrier and the main carrier. This intermediate carrier, onto which the audio information is modulated, is amplified in the amplifier ^κ and then demodulated in the demodulator y, at the output of which the audio signal is available.

On the other hand, the output signal of the Zwischenf requenzverstärkers 6 a tuned to the sound carrier of 33, '* MHz trap circuit ~ \ h and then a Farbtondemo- is m dulator fed 15 into eggs by mixing the intermediate frequency hue information and the main carrier of 3 ^ * 9 MHz one of a suppressed subcarrier of Ί, 'f MIIz modulated hue information is formed. This hue information is fed via a hue pass filter 16 to further circuit arrangements which are known per se and not shown in detail and which process this information. The signal behind the trap circuit 14 is also a. Luminance demodulator 17 is supplied with which the luminance signal modulated onto the main carrier of 3k, 9 MHz is demodulated.

'■ -, Ufert will. 009808/1235

BAD ORi & NAL

• PHN. 3k 17.

- 1 1 -

For automatic frequency control of the superimposed oscillator k , the circuit arrangement according to FIG. 3 contains a phase detector 1β to which, on the one hand, the output signal of the 5t5 MHz audio amplifier -8 and, on the other hand, the 5t5 MHz component of the output signal of the luminance demodulator 1? is fed. The sound carrier of the intermediate frequency signal , which is still allowed to some extent by the circle i'i even with correct tuning, forms an intermediate carrier of 5.5 MHz in the luminance demodulator 17 together with the main carrier. However, as a result of the trap circuit 1'4, this 5 x 5 MHz subcarrier is phase-shifted with respect to the 5t5 MHz subcarrier supplied by the demodulator 17 and Hen amplifier h, this phase shift being from the I ¹ sequence shift of the sound carrier compared to the 33t '+ MHz trap circuit is lh dependent, and thus also on the detuning of the Uberlagerungsoszil lators ^ t opposite the gate frequency properly "x ¹¹ Oszilla. The phase demodulator 1 generates a control voltage depending on the phase difference between the two 5 · 5 MHz subcarriers, and this is fed to the local oscillator via the smoothing capacitor 11 and the switch 13 to control the oscillator frequency. ICs should be noted that the two demodulators 7 and 17, the trap circuit I ^ and the phase demodulator 1b together are essentially for the automatic frequency control of the oscillator. 33, '"MHz tuned Fva qiienzdi skritninator form, this as a replacement for the tuned to the carrier frequency of 3f c, 9 MHz Frequenzdiskrimi-

009808/1235

PHN. 3 * »17 ·

"nator according to FIG. 1.

A possible embodiment of a channel switching device with a switch 13 coupled therewith is shown in FIG. In many cases, a locking wheel 19 is arranged on the spindle of the channel switching device driven by the button 12, on the circumference of which recesses 20 are provided, one for each channel to be set. A spring pawl 2 1 is arranged to cooperate with said recesses 20 and to achieve that the locking wheel 19. and so that the entire switching device assumes a fixed position on each channel. In the vicinity of the spring pawl 2 1, a contact 22 is arranged, which is electrically connected to the Paräl 1 el kondensa to.r 11 (see Fig. 1 and 3 »). The pawl 21 is electrically connected to the reference potential (ground). With the normal setting, when the pawl 2 1 lies in a recess in the locking wheel, no e 1 ektri scher is ordered. Konta "t between the ψ pawl 2 1 and the contact 22. When the switching device is switched from one to another channel, moves (He pawl out of the recess, being short Zait connected to the contact 22nd The pawl 21 and tier contact 2 2 together form the switch 13 from Fig. 1 and Ί in this way.

In many other cases the can contains 1 switching device a number of pushbuttons, with each pushbutton a previously set transmitter by actuation this push button can be selected; a locking device

009808/1235

PHN. 3417. - 13 -

device is available to hold a pressed key in this position. When actuating: another pushbutton to select a different transmitter, the locking device is moved, whereby a previously depressed pushbutton jumps back automatically. In such an I ^ analumschal t device, the invention can be implemented, for example, that with the help of the locking device, a switching contact is closed that is normally open and only closes when a push button is actuated. In some cases, for example when switching a channel from a first frequency range to a channel from a second frequency range, the construction of a switch that makes contact only during the switchover can cause difficulties. In such cases, the use of circuitry such as that shown in FIG. 5 is shown is suitable. This circuit arrangement contains, instead of a single smoothing capacitor 11 from FIGS. 1 and 3, two smoothing capacitors 11a and 11b, with a resistor 2'5a and 23b connected in parallel with each capacitor. L is. When receiving on a channel in a certain frequency range, for example, the capacitor 11a is switched on via a switch 2> 1 belonging to the range switch of the receiver. When switching to a channel of a different frequency range, the switch 2k is switched over simultaneously with the Dere i chsumschal ter, whereby the capacitor 11b for smoothing the control voltage between the frequency demodulator 10 and the oscillator k

009808/1235

PHN. 3 ^; 4 17.

is switched on dead. During the time that the capacitor 11b is effective, the capacitor 11a discharges through the Resistor .23a to the reference potential.

The switch 13 shown in Fig. 5 corresponds to the switch 13 of Figures 1 and 3 and is used to the effective Capacitor 11a or 11b for a short time during switchover from one channel to another in the same frequency range to unload.

BAS ORIGINAL 009808/1235

Claims (2)

'PHN. 3 ^ 4 17.- 13 PATENT APPLICATION. · 1.) Superposition receiver with automatic frequency control for receiving electrical transmitter signals, which has a tunable superimposing oscillator to generate a local oscillator oscillation, a mixer for mixing the received signals with the local oscillator oscillation, an intermediate frequency amplifier to amplify the output signal of the mixer, which intermediate frequency amplifier with one or more blocking circuits is provided for unifying signals from a transmitter that is adjacent in its frequency, ο j non tuned to the desired intermediate frequency frequency controller, to which the signal of the intermediate frequency amplifier is fed, and which supplies a Hegel voltage opposite a fixed IU'zugss voltage, which is supplied to the superimposed oscillator for regulating the frequency of the local oscillator via a parallel capacitor serving for smoothing / the cone voltage, as well as means for switching the frequency of the . includes local oscillator oscillation for the transition from receiving a transmitter signal on the receipt of another transmitter signal, characterized in that connected to said Parallelkondonsator further switching means (1Ί) which 2sum with said means (12) switching the frequency of the Local Oszi1latorschwingung are coupled and during this switchover the mentioned control voltage to control a * - frequency of the local (i.szi 1 ί nt'or'srhwibration to the fixed reference voltage, 009808/1235 BAB ORiGJNAL PIIN. 2. About] age rungserapf anger according to claim 1, characterized marked that the mentioned further switch tml t tel ill ') the electrical charge of the Paral lelkoiidensators during switching the frequency of the. local oscillator oscillation change in the sense that the control voltage is applied to the fixed reference voltage. 3 · heterodyne receiver according to claim 1, characterized "indicates that a first parallel capacitor (" Ma) 7 \ ir smoothing of the control voltage during dos Kmreception of a first transmitter] signal is present, and that said further switching means when switching the frequency of the local oscillator oscillation for the transition to the Receipt of another transmitter signal sets the mentioned first parallel capacitor out of operation and a second parallel capacitor (lib) to smooth the bed 1 voltage in Mefripb · k ¹ I. heterodyne receiver according to claim Ί, characterized marked, then to the two parallel capacitors K i der. «T bark (2 la, 2 1 >> connected to the voltage de. «switched off capacitor towards the reference voltage br i n ;; eri. 00980-8 / 1235 PHN. 3 ^ 17. - 17 - ABSTRACT . Overlay receiver with automatic frequency control of the local oscillator, the dem Superimposed oscillator supplied ο control voltage to the automatic Frequency control at the same time as, switchover of the Receiver from the reception of a transmitter signal to the reception of another transmitter signal on a fixed üezugspotential is placed. Q09808 / 1235