FI80547B - Tuning system for a receiver - Google Patents

Description

1 80547

The present invention relates generally to television tuning systems, and more particularly to tuning systems for a receiver for selecting a single radio frequency (RF) signal from a plurality of receivable RF signals comprising RF means (TC-1; TC). -2, LV-DTF; HV-DTF; UHF-DTF) having an adjustable frequency selective characteristic for receiving RF signals; oscillator means (LO-1) for generating an oscillator signal, the frequency of which is controlled by a first control signal to select said one RF signal; mixing means (MX) for mixing the RF signals of the RF means and said oscillator signal to generate an intermediate frequency (IF) signal at a predetermined frequency; First control means for generating a first control signal for selecting said one RD signal such that said one RF signal is shifted in frequency from said predetermined IF frequency by the mixing means; 25 tunable circuit means included in the RF means for positioning its frequency selective characteristic depending on the setting signal and means for generating the setting signal.

In many television receivers (TVs), the frequency of the local oscillator signal is controlled by a tuning voltage such that the high frequency (RF) signal corresponding to the selected channel is shifted in the mixer to a predetermined intermediate frequency (IF). This excitation voltage is generated in response to a user-selected channel by either 1) a voltage synthesizer which may include a device for comparing the reference voltage to a plurality of excitation voltages corresponding to a plurality of selectable channels, or 2) a frequency synthesizer which may include a crystal oscillator with a predetermined number associated with the channel, is adjusted by a phase-locked loop. In addition, an automatic fine tuning (AFT) feedback loop can be used to more precisely adjust the frequency of the local oscillator signal.

Tuning control circuits of the type just described usually generate band switching signals to control a plurality of filters and signal path switches associated with received TV bands, such as low VHF, high VHF, and UHF TV bands. In addition, the excitation voltage for the local oscillator: can be used roughly to adjust the frequency selectivity of certain filter circuits, such as a low-VHF, high-VHF or UHF bandpass filter.

20 Due to the normal tolerances and normal output variations of the components used in these tuning systems, it is necessary that the multiple tunable circuits in the bandpass filters, local oscillators and IF amplifier are initially adjusted to have a predetermined frequency-selective characteristic. the electronic tuning system described above may operate satisfactorily. The initial adjustment or factory setting is intended to match the frequency responses of a plurality of tuned circuits to a particular frequency response, which is necessary for the tuning system to satisfactorily respond to the user's subsequent channel selection. These adjustments, which are conventionally made by mechanically adjusting the values of inductances and / or capacitances in tuned circuits, are difficult and time consuming to make, requiring

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3 80547 road often iterative setting procedure. For practical reasons, certain functions, such as achieving a response between a certain local oscillator frequency and the tuning voltage or tracking the center frequency of a tunable filter at a selected channel frequency, cannot be set to achieve optimal performance over the entire TV frequency band. As a result, the price of the TV receiver increases substantially due to the considerable production labor involved in the setup process, and the performance of the receiver in turn decreases.

It would therefore be desirable to build a tuning system in which the need for conventional mechanical settings could be eliminated. The tuning system of the present invention makes this object possible and also provides an additional advantage by allowing the optimum performance of the setting control to be achieved over the entire TV frequency band. In addition, re-setting, if necessary, can be easily performed in the field without returning the tuning system to the factory 20 or service center.

The tuned circuits contain reactive elements such that the circuits have frequency-selective response-characteristic curves for a particular frequency or a specific frequency band. Adaptation here means adjusting the elements 25 of those circuits to change their frequency response with respect to substantially the same particular frequency or frequency band. In general, the amount of adjustment required to fit the circuit within the acceptable variance with respect to a predetermined frequency response characteristic is small and is due to the small tolerances of the values of the elements used in the tuned silicon circuits. The above is equally applicable to high-pass, low-pass, and band-pass filters, band-stop filters (e.g., trap circuits), resonant circuits for tuning oscillators, and the like.

A characteristic tuning system of the present invention for a receiver consists of means (NVMjPROM) for generating a first component of a setup signal, the first component having a plurality of values corresponding to corresponding groups of adjacent RF signals 5; means (TC) for generating a second component of the setting signal depending on the selection of said one RF signal; means (NVM; PROM) for flying the first component housing excluding the second component; means (51,52,53, R7, R8) for combining the first and second components to generate an alignment signal and supply the alignment signal to the tunable circuit means to provide a frequency selective characteristic array 15.

The present invention thus includes a plurality of tunable circuits in an RF device for adjusting the frequency selectivity in response to its plurality of control signals. The control signals are stored in memory and fed to a corresponding tunable circuit to adjust the frequency selectivity. In the drawings, Fig. 1 is a block diagram of a television receiver incorporating the present invention, Figs. 2, 3 and 4 are circuit diagrams of circuits useful in connection with the present invention, and Fig. 5 is a flow chart useful for understanding the embodiment of Fig. 1.

In the television receiver of Figure 1, the Broadcasting VHF-TV signals are received by the antenna VHF-ANT, the cable TV signals are received by the connection terminal CATV, and further by the following frequency-selective RF circuits. The TC-1 trap circuit is a filter that is fixedly tuned to attenuate another, intermediate frequency, i.e. about 46 megahertz (MHz). When the selected frequency is in the low-VHF band or the medium-band kaa-35 game television (CATV) band (54-150 MHz), the band-switching voltage 5,80547 voltage VI allows the LC-DTF of the dual-tuned filter to pass RF signals from the TC-1 to the VHF amplifier. VA. When the selected channel is in the upper part of the middle band CATV band, in the high VHF band or in the upper part of the upper band CATV band 5, in the high VHF band or in the high band CATV band (150-402 MHz), there is a band switching voltage V2 that allows double bandwidth The HV-DTF emits RF signals from the TC-1 to the amplifier VA. The RF signals from the amplifier VA are coupled to the DPX mixer MX by an RF link-10 data.

The RF signals in the UHF band (470-890 MHz) are received by the antenna UHF-ANT and further by the following frequency-selective RF circuits. The trap circuit TC-2 is a filter fixedly tuned to attenuate RF signals at a first intermediate frequency, i.e. about 416 MHz.

When the selected channel is in the UHF band, there is a band-switch field voltage V3 that allows the dual-tuned bandpass filter UHF-DTF to transmit RF signals from the TC-2 to the UHF amplifier UA. The RF signals from the amplifier UA are connected as a 20 link filter DPX to the mixer MX.

The first local oscillator LO-1 generates an oscillator signal at a frequency associated with the frequency of the selected channel signal so that the intermediate frequency signal produced by the mixer MX resulting from mixing the RF signal from the link filter DPX and the local oscillator signal is at a predetermined frequency, e.g. MHz. This intermediate frequency signal is amplified and coupled to the second mixer MA by the first IF-AMP. The IF-AMP includes a dual-tuned input filter DTF to limit the bandwidth of the intermediate frequency signal to be input to the intermediate amplifier IA. The amplified intermediate frequency signal from the amplifier IA is passed to the mixer MA by a triple-tuned bandpass output filter TTF. With a television channel bandwidth of about 6 MHz, as is the case in the United States, it is satisfactory that the DTF passband is about 12 MHz wide and the TTF passband is about 10 MHz wide. The combination of DTF, IA and TTF forms a bandpass amplifier which limits the frequencies of the signals that enter substantially amplifying from the first mixer MX to the second mixer MA.

The second mixer-amplifier MA mixes the intermediate frequency signals from the IF-AMP and the local oscillator signals 10 from the second local oscillator LO-2 to form and input the second intermediate frequency signal to the TV signal processing circuitry SP. The frequency of the signal of the local oscillator LO-2 is, for example, 370 MHz, so that the intermediate frequency signal of 416 MHz is shifted to the conventional frequency of the intermediate frequency signal of the TV, for example by about 46 to 15 MHz. The automatic fine-tuning AFT adjustment loop can be used to fine-tune the second intermediate frequency.

The TV signal processing circuit SP is conventional and supplies the demodulated video portion of the TV signal to the picture tube 20 KS for displaying a TV picture, and inputs the demodulated audio portion of the TV signal to the loudspeaker LS to play the audio program.

The channel selection and determination of the frequency of the signal of the first local oscillator LO-1 is performed as follows. The tuning control circuit TC receives the signal of the channel selected from the user input device, for example from the keypad KYBD, via the signal bus 20. (Wide arrows in Figure 1 are used to indicate that multiple signals are transmitted from one block to another; these may be digital signals, analog signals, or

combination). For example, the signal bus 20 is preferably a 2-wire digital data bus for binary coded two-digit decimal words (BCDs) to be transmitted from the keypad KYBD to the TC circuit. The encoded 35 selected channel information is further displayed in the DPY display

ti 7 80547 via bus 22 to provide digital assignment of the selected channel to the user. In response to the channel selection, the circuit TC generates a tuning control voltage VT and a band switching voltage V1, V2 and V3 depending on whether the selected channel is in the TV frequency band of the raw beam VHF, high VHF or UHF, respectively.

The first local oscillator LO-1 includes three voltage-controlled oscillators LV-LO, HV-LO and UHF-LO, corresponding to the frequency bands of low-VHF, high-VHFt 10 and UHF, respectively. Its particular oscillator associated with the frequency band containing the selected channel is enabled by the band-switching voltage V1, V2 or V3, and its oscillation frequency is controlled between the lower and upper values by the excitation voltage VT. The oscillator signal from the actuated oscillator-15 market is amplified and connected to the mixer by the MX buffer amplifier BA.

The LO-1 oscillator signal at the output terminal of the buffer amplifier BA is fed back to the circuit TC to its pre-counter point PS to provide degenerative feedback ai-20 to control the excitation voltage VT generated by the frequency synthesizer included in the circuit TC of the present tuning system. The pre-counter is a frequency divider that divides the LO-1 signal frequency by the number N, the value of which is determined in response to the channel selection indication. The frequency 25 LO-1 divided by N is compared with the reference frequency generated by the oscillator controlled by the crystal XL. The excitation control voltage VT consists of the difference signal generated by this phase comparison and is applied to the LO-1 to control its frequency, thus implementing the phase-locked loop-30 excitation system of the frequency synthesizer.

Certain specific details of the dual conversion and frequency synthesizer tuning systems described so far, although not necessarily for understanding the present invention, can be found in U.S. Patent No. 8,80547 to 4,408,348 "Tuning System For A Television Receiver", G.E. Theriault, and U.S. Patent 4,031,549, "Television Tuning System With Provisions for Receiving RF Carrier At Nonstandard Frequency," R.M.

5 Rast et al., Issued June 21, 1977.

The tunable circuits in TC-1 and TC-2 traps, LV-DTF, HV-DTF and UHF-DTF RF bandpass filters, DTF and TTF intermediate frequency filter circuits, and LV-LO, HV-LO, UHF-LO and LO-2 oscillators must all of which must be set and adapted to achieve a certain frequency-selective characteristic so that the tuning system operates satisfactorily, as described above. In this connection, the electronic control device includes a programmable read-only memory PROM which is used as a control device for storing, generating and inputing suitable control and control signals for matching the above-mentioned tunable circuits.

The read-only memory PROM comprises an uninterruptible memory NVM, the blocks of which are shown in Figure 1 by rectangles to the right of the NVM reference mark oi-20. The encoded signals, which represent several control and control signals in the form of value and binary digital words, are stored in memory locations in the NVM. The decoding and control logic DCL responds to the coded selected channel information received from the keypad KYBD via the signal bus 24, preferably as a two-digit BCD digital word, to indicate suitable memory locations in the NVM via the control bus 28. The digital-to-analog converters DAC (those shown in squares to the right of the DAC reference) receive the corresponding coded signals stored in the designated memory locations of the NVM and generate the corresponding analog control and control signals. These analog signals, typically in the voltage range of 0 to 5 volts, are amplified to extend in the range of 0 to 30 volts and are applied to a plurality of analog circuits by analog buffer amplifiers (shown by triangles to the right of the ABA reference). . The read-only memory PROM is divided into blocks marked with vertical dashed lines, corresponding to the different parts of the receiver 5 for which the control and control signals are generated. Although commercially available programmable read-only memories that are either electrically erasable type (EEPROM) or ultraviolet light erasable type (UVPROM), such as types 2816 and 2716, respectively, are available from Intel, Inc., which includes only NVM and control logic. satisfactory, it is preferable to use an integrated circuit containing at least DCL, NVM and DAC, and preferably ABA.

The preferred arrangement of the electronic control device for controlling the circuits to be tuned in the tuning system of Fig. 1 is as follows. The trap circuits TC-1 and TC-2 are each preferably double-tuned circuits. Thus, two control signals connected by two conductors on signal buses 12A 20 and 12B, respectively, are required to match each. Since the VHP and UHF channels can never be selected simultaneously, the circuits TC-1 and TC-2 never need to be operating simultaneously, so that 12A and 12B can be connected in parallel to the two-wire signal bus 12. As a result, although the read-only memory PROM provides four 25 memory location to store 8-bit digital words in NVM memory for trapped encoded signals, only two DAC converters and two ABA amplifiers are required. The DCL assigns two of the four memory locations in the NVM via the control bus 28A in response to a receive band 30 containing the selected channel.

Bandpass filters LV-DTF, HV-DTF and UHF-DTF are each double-tuned filters using two tunable circuits. Because they never need to be in operation at the same time, signal buses 14A, 14B 35 and 14C, each containing two conductors, are connected in parallel to conduct control signals from signal bus 14. As with trap control, only two DAC converters and two ABA amplifiers are required. The minimum number of memory locations required to store 8-bit-5 control signal values for bandpass filters is six, i.e., two values for each filter, for a total of three filters.

However, it is preferred that each bandpass filter be a bandpass circuit having a bandwidth of about two to five to five times the 6 MHz bandwidth of the TV channel and centered on a variable center frequency. The control signals constituting the read-only memory PROM are programmed so that the center frequency of a suitable bandpass filter is the frequency of the carrier 15 of the RF signal substantially corresponding to the selected channel. To receive 127 channels in the VHF, UHF and CATV bands, 254 memory locations are required in the NVM for 8-bit digital words, i.e. 127 values for each of the two control signals. The appropriate two memory locations are assigned via the DCL control bus 28B in response to channel selection. In addition, since the optimized control signal value can be stored for each received channel, the bandpass filters can be optimally tuned for each channel, thus avoiding the performance trade-off necessary in prior tuning systems that do not incorporate the present invention. In addition, the need for matching elements used in tunable circuits, such as capacitance diodes, as well as the need to track the tuning characteristics of multiple filters with respect to a common control signal, can be eliminated.

30 Because the bandwidth of RF bandpass filters can be relatively wide without significantly degrading the quality of TV reception, 8-bit resolution is satisfactory for NVM and DAC. This is much less, and thus much cheaper, to implement than the memory required to program the frequency of the local 80547 oscillator for channel selection, which memory needs a resolution of 12 to 14 bits. As a result, it is not necessary to make RF filters to track the offset settings at the frequency of LO-1 or LO-2 developed by the AFT control loop-5 to adjust channels transmitted on carrier frequencies that are offset by the FCC creation. (Federal Communications Commission, USA) standards for universal radio frequencies, as is often the case for CATV distribution systems.

10 Each of the local oscillators LV-LO, HV-LO and UHF-LO is set so that a certain ratio is reached between the frequency of the oscillator signal and the excitation voltage VT. Each LO includes at least two tunable matching circuits for adjusting the minimum and maximum frequency of its oscillation in response to the minimum and maximum values of the VT to correspond to the frequency range of the particular reception band in which it operates. This adjustment ensures that the phase-locked loop of the frequency synthesizer has sufficient dynamic operating range to accurately tune all 20 channels in this reception band. The two control signals can thus have two values, so that 12 memory locations in the NVM are required for 8-bit digital words, i.e. two circuits times two values times three oscillators. The two suitable locations in the NVM corresponding to the band-25 containing the selected channel are indicated by the DCL via the control bus 28C. Signal bus 16 only needs two wires for the same reason as signal buses 12 and 14; only two DAC converters and an ABA amplifier are required.

In the first IF-AMP, the filter DTF includes two tunable circuits and the filter TTF includes three tunable circuits so that a total of five matching control signals must be input via signal buses 18A and 18B. Oscillator LO-2 includes one tunable circuit and needs one match control signal from bus 18B. Since these blocks are simultaneously operating, six control signals are connected together by six wires in the signal bus 18. As before, six memory slots are used for 8-bit digital words in the NVM, six DAC converters, and six ABA amplifiers. Since these six matching adjustments are not affected by the selected channel, the DCL does not assign these six memory locations in response to channel selection.

Since the operation of the electronic control device embodying the present invention has thus been described, a setting and matching procedure by which the encoded signals are programmed into the memory locations of the NVM in the PROM will now be described.

The PROM memory NVM of the electrically erasable programmable read only memory of Fig. 1 is brought into programming mode by a mode selection signal comprising a digital "high" -15 signal applied to a terminal 26 where an otherwise "low" signal (e.g., ground) is held. The memory address signals are obtained from the TAU but are input to the DCL via the data bus 32. The eight-bit digital words input to the output lines of the assigned memory locations from the tuner control unit TAU (shown in dotted lines because it is connected only to affect the controls) via the digital data bus 30 are stored in the assigned memory locations and converted to the corresponding control and control signals.

The TAU affects the control by generating an address signal to the data bus 32, and then switching to the digital word and data bus 30 until the desired operating mode is reached, as measured at appropriate points in the tuning system by the appropriate test signals input thereto (not shown). For example, the local oscillator LO-2 can be adjusted to indicate the memory location where the word corresponding to the value of its matching control signal is stored and then monitoring the frequency of the LO-2 until the TAU has changed that value. When a frequency close to the acceptable frequency of 370 MHz has been produced, the output of that frequency shall be stored.

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i3 80547 digital word to NVM with a "low" signal at terminal 26.

As a further example, the first IF-AMP can be set by importing video and audio carrier signals from its input mixer MX and then monitoring the respective magnitudes of those carriers in the IA input as the digital words for DTF change until satisfactory corresponding magnitudes result. After these values of the matching control signal for the DTF have been stored, a similar procedure is performed for the TTF. Similarly, the trap circuits TC-1 and TC-2 can be matched by supplying a signal at the trap frequency and then changing the value of their control signals until the maximum signal attenuation is reached.

Alternatively, a wideband signal spectrum can be fed to the filter during adjustment and the resulting signal spectrum can be monitored. Although exemplary adjustments have been described above, the remaining adjustments will be apparent to those skilled in the art of television tuners. The satisfactory order of adjustments is as follows: 1. LO-2 2. L / -1 (including LV-LO, HV-L0 and UHF-LO) 3. DTF in the first IF-AMPr 4. TTF in the first IF-AMPr In AMPr 25 5. TC-1 and TC-2

6. LV-DTF

7. HV-DTF and 8. UHF-DTF.

. - It should be noted that the other order can also be used 30 satisfactorily.

Figure 2 shows, by way of example, the types of parallel tunable circuits used in the tuning system of Figure 1. Figures 2 (a) and 2 (b) show a fixed capacitance C connected in series with a mechanically adjustable inductance L '35 and a mechanically adjustable capacitance C connected in series with a fixed inductance L between terminals 40 and 42, thus forming parallel resonant circuits. The circuit of Figures 2 (a) and 2 (b) can be replaced by the electronically tuned circuit of Figure 2 (c), which avoids the mechanically adjustable elements L 'and C. The adjustable capacitance C is formed over a series combination of a fixed capacitance C and an adjustable capacitance diode CD. The capacitance of the capacitance diode CD changes inversely proportional to the es-10 preset voltage supplied from terminal 44 through a relatively high resistance R. A low-impedance bypass path for the high-frequency signals at terminal 44 is provided by a filter capacitance FC. It should be noted that a similar compensation can be made in the series resonance matching circuit.

Figure 3 (a) shows an exemplary local oscillator circuit. The NPN transistor Q is connected between the band switching voltage VB and ground and preset to its active range by voltage divider resistors RA and RB connected to its base. Its emitter circuit, including the resistance RE and the inductance LE, provides a reactance which, when reflected in the base circuit of Q, results in a negative impedance occurring between the circuit point Z and ground. A tuned circuit including a mechanically adjustable inductance L1, mechanically adjustable capacitances C1, C2, C3 and a voltage controlled capacitance diode CDT is connected between point Z and ground. The combination oscillates at about the resonant frequency of the excited circuit, which is changed by the excitation voltage VT supplied through the relative high-value resistance RT to change the capacitance of the diode CDT. In order to mix the RF signals received in the band with the selected intermediate frequency, the oscillator frequency of the LO-1 must follow a predetermined ratio to the range of values of the excitation voltage VT. Thus, adjustable elements L1, C1, is 80547 C2 and C3 are used to adjust the resonant frequency of the tuned circuit both in absolute and relative terms to the capacitance of the CDT.

The oscillator of Figure 3 (a) has been modified in Figure 5 3 (b) by adding electronically tunable matching circuits as described above in connection with Figure 2 (c). Capacitance C1 ', capacitance diode CD1 and resistance R1 replace capacitance C1; capacitance C3 ', capacitance diode CD3 and resistance R3 replace capacitance C3.

Although it has been judged satisfactory to use only a fixed capacitance C2 ', it is shown by way of example that the capacitances C4, C5, the capacitance diode CD2 and the resistances R2 and R4 can replace the adjustable capacitance C2. The control signals are applied to the capacitance diodes CD1, CD2 and CD3 from the signal bus 15 via resistors R1, R2 and R3, respectively. Since each circuit to be tuned is independently adjustable, there is no need to match the capacitance diodes used herein, and there is no need to track the responses of the oscillator and the bandpass filter to the same tuning voltage VT.

Fig. 4 shows a modification of the read-only memory PROM, in which one digital-to-analog converter DAC and an amplifier ABA ·. 'Generate control signals for several adjustable circuits in the tuning system of Fig. 1. For example, coded signals representing the values of three control signals are stored in memory locations ML-1, ML-2 and ML-3 of the NVM. These coded signals are in turn supplied to the input point of the DAC by their respective input switches IS1, IS2 and IS3 in response to the control signals supplied from the DCL via the control bus 28 via the lines 28E, 28G and 28J, respectively. In fact, switches IS1, IS2, and IS3 are channelization devices, and the wide arrows are digital data buses for inputting multiple binary signals to the DAC. After a predetermined period of time following the closure of the IS1, for example, allowing the first control signal from the DAC 35 and the ABA to settle 80547, the output switch OS1 is closed by a control signal supplied from the DCL via the control bus 28F. Closing the switch OS1 charges the charging capacitance CS1 to the voltage of the control signal, which is supplied to its corresponding tunable circuit via line 51. Switches OS1 and IS1 are then opened, after which switch IS2 and then switch OS2 are closed to generate a second control signal on line 52 and stored in charge capacitance CS2.

Switches OS2 and IS2 are then opened and the conversion-storage sequence is performed for the third control signal in capacitance CS3 and line 53. The sequence is repeated periodically to maintain the charge capacitances CS1, CS2 and CS3 at their respective control voltage levels.

Fig. 5 shows a flow chart diagram description of the operation of the DCL control logic 15 of the PROM of Fig. 1. The start 100 begins to turn on the TV receiver, in response to which the CDL, via signal buses 28A and 28D, causes the PROM to generate and input fixed matching signals 102 to, for example, TC-1, TC-2, DTF, TTF, and LO. 2. In response to channel selection 20 using the KYBD keypad, either by the user or depending on the initial predetermined channel selection when the receiver is turned on, the DCL receives and decodes the selected channel assignment received via signal bus 24. The DCL then directs the PROM to perform the sequence 106 and 116 in parallel (at the same time). The operating sequence 106 is for adjusting the local oscillator LO-1. The operation sequence 106 includes stepwise determining the band containing the selected channel 108, assigning an NVM location corresponding to LO-1 110, generating control signals corresponding to LO-1 112 using the corresponding DAC, and inputting said control signals to LO-1 using 114 the corresponding ABA and signal bus 16. The operating sequence 116 is for adjusting the bandpass filters LV-DRF, HV-DTF and UHF-DTF. The sequence of operations 116 comprises stepwise assigning the NVM location 118 of the bandpass filter corresponding to at least the selected channel i7 80547 band, generating control signals 120 in the corresponding DAC, and inputting said control signals to the bandpass filter 122 using the respective ABA and signal bus 514. in the tuning system receive the corresponding matching control signals so that the tuning system selects the selected channel for the signal processing device SP to achieve picture reproduction in the picture tube KS and to achieve sound reproduction in the loudspeaker LS. The DCL then waits for the next channel selection 124, and when such a selection is made, repeats step 104 of receiving and decoding the assigned channel assignment and operating sequences 106 and 115 to generate and input control signals. It is also satisfactory if the logic circuitry of the DCL is arranged to perform the sequences 106 and 116 in series instead of the parallel execution of Fig. 5.

Modifications to the embodiments described above are within the scope of the present invention, the invention being limited solely by the appended claims. For example, signal buses 20, 22 and 24 may be arranged to have eight wires for transmitting 8-bit parallel digital words. Further, automatic fine tuning could be provided in response to the frequency of the second intermediate frequency signal-25 I by supplying the control signal at the output of the AFT directly to the LO-1 or by supplying said control signal to the excitation control circuit TC to affect the excitation voltage VT.

Furthermore, the electronic control device according to the present invention provides flexibility in the setting of the tuning system, which has not been possible so far. For example, circuits TC-1 and TC-2 can be tuned to trap different frequencies depending on the selected channel by adding memory locations 35 reserved for trap control signal values and programming control logic DCL to assign suitable is 80547 memory locations in response to the selected channel. For example, signals close to the first intermediate frequency caused by intermodulation between the second harmonics of the video and audio carriers (about 205 and 210 MHz, respectively) of VHF channel 12 can be reduced by trapping channel 12 when channel 12 is not selected.

Thus, the number of memory locations can be selected to be between the number of RF bands and the number of TV channels. The values of the control signal 10 stored in the NVM memory locations can be modified, for example, to adjust the tuning of the bandpass filters LV-DTF, HV-DTF and UHF-DTF. One way to accomplish this modification is shown in Figure 4, where the control signal in line 54 includes a portion fed through resistor R7 from line 52 and generated in response to coded signals stored in the NVM and a portion fed through resistor R8 and formed at terminal 56 in response to a control signal. It can further be appreciated that the latter part - could be responsive to the tuning voltage VT, for example, so that the tuning of the RF bandpass filters is at least partially responsive to the selected band. In particular, the digital words stored in the NVM can be programmed to correspond to values determined by the relationship between the actual LO-1 tuning voltage and the frequency response of the selected channel so that the control signals generated by the PROM and fed to the bandpass filters provide the frequency to which the bandpass filters are tuned. frequency in response to the LO-1 tuning voltage. That is, the LO-1 tuning voltage is modified and applied to the band-30 dance filters so that they track the selected channel without the need to select varactor diodes or attempt to set those filters by mechanical means.

Although the present invention has been described in the context of a dual conversion tuning system in which the received signals are mixed twice, i.e. by mixers MX and MA,

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i9 80547 could just as advantageously be used in single-conversion tuning systems used in most commercial TV receivers currently on the market. In addition, the present invention can be satisfactorily used in a frequency synthesizer tuning system, as described herein, as well as in a voltage synthesizer tuning system, signal retrieval, or memory tuning systems.

Claims (3)

20 80547 A tuning system for a receiver for selecting a single radio frequency (RF) signal from a plurality of receivable RF signals, comprising RF means (TC-1? TC-2, LV-DTF; HV-DTF; UHF-DTF) having an adjustable frequency selective characteristic for receiving RF signals; oscillator means (LO-1) for generating an oscillator signal 10, the frequency of which is controlled by the first control signal to select said one RF signal? mixing means (MX) for mixing RF signals of the RF and said oscillator signal to generate an intermediate frequency (IF) signal at a predetermined frequency; first control means for generating a first control signal to select said one RF signal such that said one RF signal is shifted in frequency from said predetermined IF frequency by the mixer means; tunable circuit means included in the RF means for setting its frequency selective characteristic depending on the setting signal, means for generating a setting signal, means (NVM; PROM) for generating a first component of the setting signal, the first component having a plurality of values corresponding to adjacent RF signals; and means (TC) for generating a second component 30 of the setting signal depending on the selection of said one RF signal; characterized by means (NVM; PROM) for storing the first component excluding the second component; 35 means (51,52,53, R7, R8) for combining the first and second II 21 80547 components to generate an alignment signal and supply the alignment signal to the tunable circuit means to provide a frequency selective characteristic array. A tuning system according to claim 1, characterized in that the storage medium is a digital memory with a plurality of memory locations for storing data representing the first component of the setting signal. A tuning system according to claim 1, characterized in that the means for generating the second component of the setting signal generates a second component depending on the first control signal, and the means for combining includes a plurality of resistors for combining the first and second components of the setting signal in a predetermined ratio. 22 80547