GB2286301A

GB2286301A - Digital voltage-tuning method for a broadcast receiver

Info

Publication number: GB2286301A
Application number: GB9501121A
Authority: GB
Inventors: Il-Ku Na
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1994-02-07
Filing date: 1995-01-20
Publication date: 1995-08-09
Anticipated expiration: 2015-01-20
Also published as: DE19500720A1; KR0138330B1; GB2286301B; GB9501121D0; KR950026219A

Description

C.

2286301 DIGITAL VOLTAGE-TUNING METHOD FOR A BROADCAST RECEIVER The present invention relates to a digital voltagetuning method for a broadcast receiver, and particularly, but not exclusively, to a digital voltage-tuning method for a broadcast receiver which improves the nonlinearity characteristic of a tuning voltage.

As an electronic tuning device of such broadcast 10 receivers as a video cassette recorder or television, there are in existence both frequency synthesizing systems and voltage synthesizing systems. Voltage synthesizing systems select the desired frequency by means of applying a voltage to a tuner. The principle of the voltage is synthesizing system is that a varactor diode is used as a tuning capacitor in an LC tank circuit and a tuning voltage is applied across the varactor diode. Thus, the capacitanc:e of the varactor diode is varied depending on the tuning voltage, thereby tuning the desired frequency.

The tuning voltage is generated as follows. Tuning data is increased or decreased to approach the desired channel when a channel is selected. Then, a pulse width modulation signal based on the tuning data is generated, and a tuning driving voltage is pulsed by the pulse width modulation signal. Then, the resulting intermittent to.

- 2 voltage is integrated, thereby generating a tuning voltage.

Conventional tuning data increases linearly since a step is constant. However, the tuning voltage corresponding to conventional tuning data has nonlinearity characteristics since an integration characteristic of the intermittent voltage is non-linear and the output characteristic of the varactor diode is also non-linear. Therefore, even though the tuning data may change linearly the tuning voltage has a non-linear characteristic, the tuning voltage being greatly increased ifi the steep slope portion of the non- linear curve. Thus, a tuning error is caused during tuning.

It is an aim of preferred embodiments of the present invention to provide a digital voltage-tuning method for a broadcast receiver that can improve a non-linearity characteristic of a tuning voltage.

It is another aim to provide a digital voltage-tuning method for a broadcast receiver that equally improves an automatic fine tuning range of each channel.

il v.

According to a first aspect of the invention, there is provided a digital voltage-tuning method for a broadcast receiver comprising the steps of:

dividing a tuning voltage curve into a plurality of sections and preparing a compensating parameter for each section, in order to compensate a non-linear characteristic of a tuning voltage curve of each band to provide a substantially linear characteristic; generating tuning data having a non-linear characteristic by utilising the relevant compensating parameter according to the section of the band to which a selected channel belongs; generating a pulse width modulation signal in accordance with the generated tuning data; employing said generated pulse width modulation signal to pulse a tuning driving voltage to provide an intermittent voltage; and integrating said intermittent voltage so as to generate a tuning voltage of said selected channel.

(0, Preferably, the step of preparing a compensating parameter comprises the steps of:

(a) checking a band; (b) calculating a frequency change value f or each step with respect to the entire section of the checked band within a predetermined resolution; (c) calculating an average pulse width change value, i.e., rate of said calculated frequency change value for each step to a predetermined frequency change value for one step of pulse width change; is (d) calculating an average step value with respect to the entire section of said checked band by said calculated average pulse width change value within said predetermined resolution; (e) checking a non-linearity compensation section depending on the slope of the tuning voltage curve within said selected band; (f) repeatedly performing, for all thesections, obtaining a pulse width change value and a step value of the corresponding section by employing said corresponding 11 gab 1W band width change value and average step value according to the slope of the corresponding section of said tuning voltage curve in response to said checked compensation section; and (g) repeatedly performing said steps (a) to (f) for each band after obtaining the pulse width change value and the step value f or all the sections so as to obtain the pulse width change value and the step value for each 10 section of all bands.

Preferably, said tuning data generating step cbmprises the steps of:

(a) checking to which band said selected channel frequency belongs; (b) initializing a step value and time counter of the first section of the relevant band; (c) generating tuning data depending on said step value and time counter; (d) checking whether there is a video signal received via the channel tuned to by means of the tuning voltage corresponding to said tuning data; J61A W (e) incrementing said step value and time counter if there is no video signal received; (f) performing said steps (c) and (d) until said incremented step value becomes larger than said step parameter of the first section; (g) repeatedly performing steps (c) and (d) by employing the respective calculated parameter of each next section whenever said step value becomes larger than the calculated parameter so as to tune the selected channel through all the sections of the checked band; and (h) determining the selected channel if there is a received video signal and performing an automatic fine tuning.

According to a second aspect of the invention, there is provided a digital voltage-tuning method for a broadcast receiver, wherein a tuning circuit portion of the broadcast receiver comprises a tuner for receiving an RF signal and outputting an IF signal, a demodulating circuit for receiving, detecting and demodulating the IF signal from the tuner to output a video signal, a sync- detector for detecting a sync signal of the video signal, a controller for receiving an output from the sync 0 detector and providing a pulse width modulated signal to a tuning voltage driving circuit, which tuning voltage driving circuit processes the pulse width modulation signal to provide a voltage tuning signal to the tuner to thereby enable automatic tuning, the tuning voltage driving circuit having a non-linear transfer characteristic such that linear variations in duty ratio of the pulse width modulation signal produce non-linear variations in tuning voltage, the method being characterised in that tuning data in the form of the pulse width modulation signal is generated in a non-linear fashion by the controller so as to render the tuning v61tages output from the tuning voltage driving circuit to be compensated so as to vary in a substantially linear fashion.

The method may further comprise, any one or more of the features from the accompanying specification, claims, abstract and/or the drawings in any combination.

The invention includes a broadcast receiver incorporating a tuning circuit operating in accordance with the method of the first or second aspects.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which:

Figure 1 is a block diagram of a broadcast receiver that has an electronic tuner adopting a general analog AFT system; Figure 2 is a block diagram of a broadcast receiver having a tuner adopting a general full digital system; Figure 3 is a detailed circuit view of the tuning voltage driving circuit shown in Figure 1 and Figure 2; Figure 4 is a graph illustrating the conventional relationship between tuning voltage and the duty of pulse width modulation signal; Figure 5 is a graph illustrating the relationship between tuning voltage and the duty of the pulse width modulation signal, according to embodiments of the present invention; Figure 6 is a graph illustrating the relationship between tuning voltage and the duty of the pulse width A^ W modulation signal, according to an embodiment of the present invention; Figure 7 is a flowchart illustrating a program for calculating a correction parameter, according to embodiments of the present invention; and Figure 8 is a flowchart illustrating the tuning operation performed utilising the calculated correction 10 parameter.

The present invention will be explained in more d(.-tail with reference to the attached drawings.

First, the general electronic voltage-tuning system will be explained prior to the explanation on an embodiment of the present invention.

Figure 1 is a block diagram of a broadcast receiver that has an electronic tuner adopting an analog AFT system. A tuner 10 receives a radio frequency (RF) signal via an antenna, coaxial cable or the like, and outputs an intermediate frequency (IF) signal if a broadcast signal is present at the frequency selected by an applied tuning voltage VT. A demodulation circuit 20 receives, demodulates and detects the IF signal to output a video úA W signal and outputs an automatic frequency tuning (AFT) signal for performing a fine tuning so as to centre on the peak of the received signal. The AFT signal is applied to an AFT driving circuit 30 to be output as a suitable fine tuning signal. The output f ine tuning signal is applied to tuner 10 via an AFT switch 40. A sync-detector 50 detects a sync signal in order to determine whether a video signal is received. A controller 60 generates an AFT on/off signal so as to control the switching operation of AFT switch 40 and, when a desired channel is selected, increases the tuning data in order to tune the channel and generates a pulse width modulation signal whose duty ratio it increased depending on the tuning data. However, when a signal indicating sync signal detection is supplied from sync-detector 50, controller 60 recognizes a tuning proximity, holds the current duty ratio of the pulse width modulation signal and closes AFT switch 40 so that an auto fine tuning operation can be perfEormed. A tuning voltage driving circuit 70 generates a tuning voltage (VT) whose voltage varies in response to the duty ratio of a pulse width modulation signal (PWM) from controller 60.

It should be noted that the above AFT analog method needs an AFT switch.

Figure 2 is a block diagram of a broadcast receiver having a tuner adopting a full digital system. The method of Figure 2 differs from that of Figure 1 as follows. In Figure 2, controller 60 receives an analog AFT signal to be converted into a digital signal so that automatic frequency tuning can be performed digitally, and generates a pulse width modulation signal that corresponds to AFT digital value. Thus, fine tuning is performed digitally. Accordingly, controller 60 varies the duty ratio of the pulse width modulation signal until the duty ratio becomes the center of AFT voltage and holds the then duty ratio, thereby performing a fine tuning via software. Therefore, the AFT switch can be removed.

Figure 3 is a detailed circuit view of the tuning voltage driving circuit 70. A tuning driving voltage, for example, 33V, is switched by the pulse width modulation signal applied to a switching circuit 72 to give an intermittent voltage output. A multi-stage integrator 74 integrates the resulting pulsed 33V so as to generate an average tuning voltage (VT). Thus, the tuning voltage can be plotted as the non-linear characteristic curve shown in Figure 4. The non-linearity is the result of the integration characteristics of multi-stage integrator 74.

Meanwhile, the duty ratio of the pulse width modulation signal is linear with respect to the tuning data. In general, the conventional method for establishing the tuning data is as follows.

Table 1 band channel frequency range number VHF-low E02-SO1 48.25105.25MHz VHF-high S02-S20 112.25294.25MH z UHF 21-69 471.25855.25MH z In a low band, the frequency change for each step is equal to the channel's bandwidth divided by the resolution, that is, (107.25MHz - 46. 25MHz)12 14 or 4MHz. 15 Then, APWM can be expressed as follows.

APWM = 5 0 1Cqz 4R272 # 12 Accordingly, the STEP value can be expressed as follows.

where R is resolution in b STEP R A PWM = 1365 its.

qw Therefore, the APWM and STEP values, which are obtained with respect to the high band and UHF band by employing the same method as that used in the low band, can be arranged as follows.

Table 2

Fband received frequency APWM STEP EVHF-high 11 VHF-low 46.25-107.25MHz 12 1365 V - 1 01 110.25296.25MHz 5 3276 lg U 469.25-857.25MHz 2 8192 UHF Therefore, in the conventional method, the tuning data increases linearly in each band. However, the tuning voltage generated by the pulse width modulation signal generated by the linear tuning data has a non-linearity as shown in Figure 4. Here, duty increments S1 and S2 of the pulse width modulation signal are small, while the corresponding tuning voltages AV1 and AV2 exhibit greater changes.

characteristic In the conventional method, the tuning voltage changes non-linearly when the duty ratio of the pulse width modulation signal increases by regular steps due to the non-linearity characteristics of the varactor diode of the tuner and the integration characteristic of the tuning voltage driving circuit. Thus, the operating range of AFT is different for each channel. In addition, a tuning error - 14 is caused by a rapid voltage increase occurring at higher tuning voltages.

Embodiments of the present invention enable a compensation of a nonlinearity characteristic of the tuning voltage into one exhibiting linear characteristics over variations in the duty of the pulse width modulation signal, as shown in Figure 5, so that a constant operating range of the AFT function can be maintained for all channels.

In an embodiment of the present invention, the rtlationship between the duty ratio change and the tuning voltage of the pulse width modulation signal is correctly analyzed in order to ensure an adequate AFT operating range for each channel. Then, as shown in Figure 6, the correction parameter for generating the tuning data can be calculated by being based on the approximated correction characteristic, as follows.

For the VHF-low band:

1) in section 1 (0 to C) where the average APWM is doubled and the STEP value is halved due to the slope of section 1 being twice that of the 0to-D section of the tuning curve. APWM = 12 X 2 = 2 4 STEP = average step X (7/32) X (12/24) = 149 2) in section 2 (C to B) where the average APWM and the STEP value multiplied by one. APWM = 12 X 1 = 12 STEP = average step X (10117) X (12/12) = 472 3) in section 3 (B to A) where the average Apwm is halved and the STEP value is doubled.

APWM = 12 X (l/2) = 6 STEP = average step X (15/32) X (12/6) = 1280 For the VHF-high band:

1) section 1 APWM = 5 X 2 = 10 STEP = average step X (7/32) X (5/10) = 358 2) section 2 APWM = 5 X 1 = 5 STEP = average step X (10/32) X (5/5) = 1024 3) section 3 APWM = 5 X (l/2) = 3 STEP = average step X (15/32) X (5/3) = 2559 For the UHF band:

1) section 1 APWM = 2 X 2 = 4 STEP = average step X (7/32) X (2/4) 896 2) section 2 APWM = 2 X 1 = 2 STEP = average step X (10132) X (212) 2560 3) section 3 APWM = 2 X (l/2) = 1 STEP = average step X (15/32) X (2/1) 7680 The above expressions can be presented as a table.

Table 3 band section received frequency APWM STE p 1 24 149 VHF-low 46.25107.25MHz 2 12 472 3 6 128 0 1 10 358 VHF- 110.25296.25MHz high 2 5 102 4 3 3 255 9 1 4 869 UHF 469.25867.25MHz 2 2 256 0 3 1 7 0 The general expression for calculating a parameter of the present invention is as follows.

AF - Ft W... (1) STEP R where AFST5P is the frequency change for each step and Fb, 'S bandwidth.

1 - 17 z 0 RE2 ApwM,', = A... (2) where APWM.,., is the average change in the pulse width modulation signal.

R ve A PWM,', where STEP,,, is the average step value.

STEpa - ---(3) Apwm = APWM, ,. x S... (4) where S is the slope of each section of the curve.

STEP = STEpave D 'X Apwmae A j APWM where DUTY is the duty ratio of each section and A is the overall PWM duty ratio (see Figure 6).

Figure 7 is a flowchart illustrating a program for calculating correction parameters according to an 10 embodiment of the present invention.

The step for obtaining the compensating parameter is performed as follows. First, the band to be obtained is checked by employing a correction parameter (100A and lOOB). If it is a VHF-low band, step 100 is performed, if it is a VHF-high band, step 200 is performed, and if it is a UHF band, step 300 is performed. The detailed process for each band is as follows.

- is - In step 102, the frequency change value for each step of the VHF-low band is obtained within the given resolution by employing expression (1). In step 104, an average pulse width change value IPWM by the calculated frequency change value for each step is obtained by employing expression (2). In step 106, an average step value is obtained by the calculated average APWM within the given resolution by employing expression (3).

A slope is checked (step 108) so as to obtain APWM and STEP(L1) of section 1, and the calculation result of STEP(L3) is checked (step 122), and if STEP(L3) is checked at not calculated, the process is fed back to step 108.

Then, APWM and STEP(L2) for section 2 is obtained (steps 114 and 116) and fed back to step 108. Then, APWM and STEP(L3) for section 3 is obtained (steps 118 and 120).

Since STEP(L3) is calculated in step 122, the program ends.

Step 200 is performed for the VHF-high band in the same manner as that employed for step 100. Step 300 is performed for the UHF band.

The tuning method after parameters for each section of each band are calculated will be explained with reference to Figure 8.

1 A check is performed in order to determine to which band the desired channel frequency belongs (step 802), and if it belongs to a f irst band, a step value and a time counter (N) are initialized (step 804). Then, the pulse width modulation signal is generated by the relevant calculated pulse width change parameter (step 806). Then, a check is performed by detecting a sync signal in order to determine whether there is the video signal received by the tuning voltage generated by the pulse width modulation signal (step 808). If there is no video signal, the step value and time counter are incremented (step 810). Then, the process returns to step 806 and the loop is repeated uhtil the increased step value becomes larger than the calculated step parameter of section 1 (step 812). That is, steps 806 to 812 are for performing the tuning of section 1 with the increase of steps.

If the step value is larger than the calculated STEP(L1) parameter, the desired channel does not exist in section 1. Therefore, the time counter is re-initialized (step 814).

The same process as that repeatedly performed in the pulse width modulation signal generating step is performed repeatedly, using the calculated parameter of section 2, AA CV - 20 until there is no video signal detected and the increased step becomes larger than the step parameter (step 816).

If the step value is larger than the calculated STEP(L2) parameter, it is determined that the desired channel does not exist in section 2. Therefore, the time counter is re-initialized (step 818).

The same process as that performed for section 2 is performed repeatedly for section 3 (step 820).

In the repeatedly performed process for varying the pUlse width modulation signal for each section, the detected video signal indicates the fact that the desired is channel is near. Then, an AFT signal is received, and an auto fine tuning is performed by the received AFT data (step 822). Then, the general operation for device is performed (step 1100), and the program ends.

If the step is larger than the step parameter of section 3, the desired channel does not exist in the band. Therefore, the general operation for device is performed (step 1100), and the program ends.

0 Tuning is performed f or the VHF-high band by the same process as step 800 (step 900). Tuning is also performed for the UHF band (step 1000).

As may be seen from the above, in embodiments of the invention tuning is performed in a manner by which tuning data is generated non-linearly so that a tuning voltage can be generated substantially linearly. Thus, the AFT operating range can be set equally for all channels and a tuning error can be reduced.

The reader's attention is directed to all papers and dbcuments which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

AA W 22 - Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

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Claims

CLAIMS 1. A digital voltage-tuning method for a broadcast receiver

comprising the steps of:

dividing a tuning voltage curve into a plurality of sections and preparing a compensating parameter for each section, in order to compensate a non-linear characteristic of a tuning voltage curve of each band to provide a substantially linear characteristic; generating tuning data having a non-linear characteristic by utilising the relevant compensating p&rameter according to the section of the band to which a selected channel belongs; is generating a pulse width modulation signal in accordance with the generated tuning data; employing said generated pulse width modulation signal to pulse a tuning driving voltage to provide an intermittent voltage; and integrating said intermittent voltage so as to generate a tuning voltage of said selected channel.

0 - 24
2. A digital voltage-tuning method for a broadcast receiver according to claim 1, wherein the step of preparing a compensating parameter comprises the steps of:

(a) checking a band; (b) calculating a frequency change value for each step with respect to the entire section of the checked band within a predetermined resolution; (c) calculating an average pulse width change value, i.e., rate of said calculated frequency change value for eAch step to a predetermined frequency change value for one step of pulse width change; (d) calculating an average step value with respect to the entire section of said checked band by said calculated average pulse width change value within said predetermined resolution; (e) checking a non-linearity compensation section depending on the slope of the tuning voltage curve within said selected band; (f) repeatedly performing, for all the sections, obtaining a pulse width change value and a step value of to the corresponding section by employing said corresponding band width change value and average step value according to the slope of the corresponding section of said tuning voltage curve in response to said checked compensation section; and (g) repeatedly performing said steps (a) to (f) for each band after obtaining the pulse width change value and the step value for all the sections so as to obtain the 10 pulse width change value and the step value for each section of all bands.
3 '. A digital voltage-tuning method for a broadcast receiver according to claim 1 or 2, wherein said tuning is data generating step comprises the steps of:

(a) checking to which band said selected channel frequency belongs; (b) initializing a step value and time counter of the first section of the relevant band; (c) generating tuning data depending on said step value and time counter; (d) checking whether there is a video signal received via the channel tuned to by means of the tuning voltage corresponding to said tuning data; (e) incrementing said step value and time counter if there is no video signal received; (f) performing said steps (c) and (d) until said incremented step value becomes larger than said step 10 parameter of the first section; (g) repeatedly performing steps (c) and (d) by einploying the respective calculated parameter of each next section whenever said step value becomes larger than the is calculated parameter so as to tune the selected channel through all the sections of the checked band; and (h) determining the selected channel if there is a received video signal and performing an automatic fine tuning.
4. A digital voltage-tuning method for a broadcast receiver, wherein a tuning circuit portion of the broadcast receiver comprises a tuner for receiving an RF signal and outputting an IF signal, a demodulating circuit for receiving, detecting and demodulating the IF signal 1 (0 - 27 from the tuner to output a video signal, a sync-detector for detecting a sync signal of the video signal, a controller for receiving an output from the sync detector and providing a pulse width modulated signal to a tuning voltage driving circuit, which tuning voltage driving circuit processes the pulse width modulation signal to provide a voltage tuning signal to the tuner to thereby enable automatic tuning, the tuning voltage driving circuit having a non-linear transfer characteristic such that linear variations in duty ratio of the pulse width modulation signal produce non-linear variations in tuning voltage, the method being characterised in that tuning data in the form of the pulse width modulation signal is generated in a non-linear fashion by the controller so as is to render the tuning voltages output from the tuning voltage driving circuit to be compensated so as to vary in a substantially linear fashion.
5. A digital voltage-tuning method according to claim 4, wherein the method further comprises, any one or more features from the accompanying specification, claims, abstract and/or drawings in any combination.
6. A digital voltage-tuning method for a broadcast receiver substantially as hereinbefore described with reference to the accompanying drawings.

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7. A broadcast receiver incorporating a tuning circuit operating in accordance with the method of any of the preceding claims.

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