KR100565679B1 - AGC apparatus in digital TV receiver - Google Patents

Abstract

A AGC device of a digital TV receiver, comprising: a pass band / base band data selector configured to select an input passband signal or a feedback baseband signal; a power value and a set reference value of an input signal that is digitally converted to remove a DC component An external AGC unit for detecting a gain error value by a signal Pb_ref and outputting an AG AG control signal for controlling an external gain by an AGC step signal, and an IF AGC control signal; It includes an internal AGC unit for controlling the gain in the receiver by using the signal selected by the band / base band data selection unit.

Internal AGC, External AGC, AM Hum, AGC LOCK Detector, Digital Domain

Description

Automatic gain control device for digital TV receivers {AGC apparatus in digital TV receiver}

1 is a block diagram illustrating a digital TV including a general AGC device

2 is a signal waveform diagram showing an AM hum generated by power supply noise

3 is a signal waveform diagram of removing AM hum by automatic gain control in the digital domain.

4 is a block diagram of a digital TV receiver to which the automatic gain control device according to the present invention is applied.

5 is a block diagram of an automatic gain controller for removing AM Hum in the digital domain.

6 is a detailed block diagram of an internal AGC block for removing AM Hum in the digital domain.

Explanation of symbols for the main parts of the drawings

101. Tuner 102. SAW Filter

103.IF Amplification and Downconverter 200.VSB / QAM / OOB Receiver

201.A / D Converter 202.RF and IF AGC Signal Generator

203. Phase division and complex multiplier 204. Resampler and matched filter

205. Pass band / base band data selector

206. Internal AGC

The present invention relates to an automatic gain control (AGC) apparatus in a digital TV receiver using a VSB / QAM / OOB scheme.

Digital TV is a TV system developed to let you feel the impression of a theater in your room. Compared to current analog TVs, the screen resolution is much higher, wider in the horizontal direction, and CD-level sound is supplied in multiple channels.

These digital TVs are promoting their standardization by preparing their own broadcasting methods and standards in the United States, Europe, and Japan. In the United States, the transmission format adopts the residual sideband (VSB) method proposed by Zenith in the United States, the compression format adopts MPEG (MPEG) for video compression, and Dolby AC-3 for audio compression. The format is specified to be compatible with existing display methods.

On the other hand, although the gain of the broadcast signal transmitted from the transmitter is always constant, the gain of the signal varies due to the distance to the digital TV receiver and through various channels until reaching the receiver. do.

The gain-modulated signal is input to the receiver, and most of the digital parts of the receiver are designed assuming that the signal is always input with a constant magnitude of gain. Therefore, it is necessary to adjust the gain of the analog signal input to the digital TV receiver so that the gain always has a certain magnitude, and then convert it into a digital signal.

It is the Automatic Gain Control (AGC) device that plays this role. The AGC device determines the gain of the current input signal by looking at the average or power of the input signal. In this case, the amplifier is controlled in an analog circuit of RF (high frequency) and IF (intermediate frequency) terminals according to the determined gain so that the signal has a desired size.

Most AGC devices currently used use a delayed AGC scheme as shown in FIG. 1.

1 is a block diagram of a digital TV including a general AGC device.

First, when a high frequency (RF) signal modulated in the manner of VSB, QAM, OOB, etc. is received through an antenna, the tuner 101 converts an RF signal of 40 to 860 MHz into a first IF signal of 44 MHz, and then The signal is output to the SAW filter 102 employed as a function of cancellation and noise signal removal. Here, the output size of the tuner 101 is adjusted by the RF amplifier stage in the tuner 101.

At this time, since all information exists in the 6 MHz band from the intermediate frequency of 44 MHz, for example, the SAW filter 102 removes only the 6 MHz band in which the information exists from the output of the tuner 101 and removes all remaining sections. Output to IF amplification and down converter 103.

The IF amplification and down converter 103 receives an oscillation frequency (not shown) for generating the second IF signal, downconverts the signal filtered by the SAW filter 102 into the second IF signal, and then VSB / QAM. Output to / OOB receiver 104.

In this case, the first IF signal is output to the VSB / QAM / OOB receiver 104 after the gain is controlled by the IF amplification and down conversion unit 103. That is, the IF amplification and down converter 103 controls the gain of the first IF signal to be the signal size required for down-conversion or digitization of the received signal by the VSB / QAM / OOB receiver 104.

The VSB / QAM / OOB receiver 104 digitizes the second IF signal whose gain is controlled after VSB / QAM / OOB demodulation. At the same time, the VSB / QAM / OOB demodulated signal is output to the AGC signal generator 100 for AGC.

The AGC signal generator 100 stores, for example, information used for gain adjustment from the beginning of the operation of the receiver to the present. When the VSB / QAM / OOB demodulated signal is input, the AGC signal generator 100 compares the previously stored gain information. If the gain of the received signal is small, an IF AGC signal for increasing the gain is generated, or if the gain is large, an IF AGC signal for reducing the gain is generated and fed back to the IF amplification and down converter 103.

The IF amplification and down converter 103 raises or lowers the gain of the first IF signal according to the input IF AGC signal so that the gain of the first IF signal is in a desired state.

That is, the method of controlling the actual gain is first set to have the maximum gain that the receiver can have when the power is turned on or when the channel is changed, and then the IF amplification and down converter ( First adjust the gain.

If the gain control capability of the IF amplification and down converter 103 reaches a limit and the output signal of the VSB receiver 104 is not the desired size, the AGC signal generator 100 is delayed back to the tuner 101. The delayed RF AGC signal is transmitted to automatically adjust the gain of the tuner 101.

The gain fluctuates due to the noise generated by the power source noise and other devices caused when the AC power source is converted to the DC power source. This phenomenon is called AM hum.

2 is a signal waveform diagram showing an AM hum generated by power supply noise.

This is expressed as an equation.

The AM hum is an AGC in the tuner 101 and the IF amplification and down converter 103 which are analog elements in front of the VSB / QAM / OOB receiver 104 which digitizes the received signal in the automatic gain control apparatus according to the prior art. AM hum removal in the analog domain is possible by performing.                         

The signal from which the AM hum is removed in the analog domain is input to the VSB / QAM / OOB receiver 104, and the non-linear characteristics of the elements constituting the VSB / QAM / OOB receiver 104 are provided. Due to this, it is likely that AM hum is generated in the signal while passing through the VSB / QAM / OOB receiver 104.

However, at present, there is a problem that AM hum generated in the VSB / QAM / OOB receiver 104 cannot be removed.

The present invention has been made to solve the above problems, to provide a digital TV automatic gain control device that can remove the AM hum (Hum) more stably by performing AGC in the digital domain as well as the analog domain. The purpose is.

Automatic gain control apparatus for a digital TV receiver according to the present invention for achieving the above object is a pass band / base band data selection unit for selecting the input pass band signal or the feedback baseband signal; The external AGC outputs an RF AGC control signal and an IF AGC control signal for detecting a gain error value by removing the power value of the inputted signal and the set reference signal Pb_ref and controlling the external gain by the AGC step signal. And an internal AGC unit which is driven by the AGC step signal and controls gain in the receiver using a signal selected by the pass band / base band data selection unit.

Here, the AGC LOCK detection unit for detecting the convergence time of the automatic gain control loop using the AGC gain error output from the external AGC unit, and generates an AGC step signal to control the loop gain of the automatic gain control loop.

The signal whose gain is controlled in the receiver by the internal AGC unit includes a Hilbert transformer for separating the phase of the gain-controlled signal, and complex multiplication of the phase-separated signal with a complex carrier proportional to the phase error. A complex multiplier that transitions to a band signal, a resampler and matched filter unit that generates a sample that is twice the symbol frequency in the output signal of the complex multiplier, and performs filtering to recover the signal to a previously transmitted character; It is characterized in that the feedback to the pass band / base band data selector through a multiplier to multiply the value for matching the gain of the base band signal output from the filter unit.

And an internal AGC unit comprising a squarer that squares an input signal and a subtractor that obtains a difference between a power value of a squared received signal and a reference power value and obtains a gain error value; when the gain error value is input, an AGC step signal is input to the AGC step signal. A loop filter comprising an LSHIFT register for adjusting a bandwidth of the feedback loop, an adder and a delay element for accumulating a bandwidth-adjusted gain error value; a value corrected by multiplying a pass band signal by a cumulative gain error value output from the loop filter; It consists of a multiplier that outputs and a delay element that delays the output signal of the multiplier and feeds it back to the pass band / base band data selector to remove AM Hum in the digital domain.

Here, the MUX may further include selecting a corrected passband signal and a passband signal by the internal AGC bypass signal to determine whether to bypass the passband signal or to pass the internal AGC unit.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, with reference to the accompanying drawings illustrating the configuration and operation of the embodiment of the present invention, the configuration and operation of the present invention shown in the drawings and described by it will be described as at least one embodiment, By the technical spirit of the present invention described above and its core configuration and operation is not limited.

3 is a signal waveform diagram in which AM hum is removed by automatic gain control in the digital domain, and FIG. 4 is a block diagram of a digital TV receiver to which the automatic gain control apparatus according to the present invention is applied.

The present invention can remove AM Hum as shown in FIG. 3 by performing automatic gain control in the digital domain by selectively using a passband signal and a baseband signal while controlling gain of external devices when AM Hum is generated. It is.

4 illustrates a configuration of a digital TV receiver according to the present invention. The VSB / QAM / OOB receiver 200 includes an A / D converter 201 for converting an analog intermediate frequency signal to digital, and the A / D converter. An RF and IF AGC signal generator 202 for outputting an IF AGC control signal and an RF AGC control signal using the digitized intermediate frequency signal output from the 201 and the digitalized through the A / D converter 201. The signal of the passband is divided into I and Q signals, and a complex carrier in the form of a sinusoidal wave (SIN) and a cosine wave (COS) has been received, and multiplied by the I and Q signals of the passband, respectively, A phase division and complex multiplier 203 for transitioning Q signals to baseband I and Q signals, and an input signal for generating a sample corresponding to twice the symbol frequency and recovering the signal with the transmitted character. Resume matches the filter used to Pass / band selects one of a multiplexer and matched filter unit 204, a baseband signal from the resampler and matched filter unit 204, and a passband signal from the A / D converter 201. A baseband data selection unit 205 and an internal AGC unit 206 for controlling gain in the receiver 200 by using the signal selected by the passband / baseband data selection unit 205.

In FIG. 4, the tuner 101, the SAW filter 102, and the IF amplification and down converter 103 are analog front-end parts, and their configuration and operation are the same as those in FIG. The detailed description is omitted.

In the automatic gain controller according to the present invention, the part for AM Hum removal in the digital domain will be described in more detail as follows.

5 is a block diagram of an automatic gain controller for removing AM Hum in the digital domain.

First, an A / D converter 501 for converting a gain-controlled signal into a digital signal in the analog domain, a DC canceller 502 for receiving a digitally converted signal and removing a DC component generated in the conversion process or externally, and a gain error. A pass band / base band data selector 503 for selecting a pass band signal or a base band signal from which the DC component has been removed to detect a signal, and a DC component by the DC canceller 502. An external AGC unit 511 which receives the removed passband signal and outputs an RF AGC control signal for controlling external gain by the reference signal Pb_ref and the AGC step signal of the passband signal, and an IF AGC control signal; AGC LOCK detector for detecting the convergence point of the automatic gain control (AGC) loop using the AGC gain error output from the external AGC unit 511 and generating the AGC step signal to control the loop gain of the automatic gain control loop ( 512, an internal AGC unit 504 that receives the signal selected by the pass band / base band data selection unit 503 and performs automatic gain control in the digital domain inside the chip by an AGC step signal, and an internal AGC unit 504. Hilbert transducer 505 that phase-converts the phase of the gain-controlled signal by 90 ° to separate the real and imaginary components, and the phase-separated signal proportional to the phase error of the NCO (Numerically Controlled Oscillator) 506. A complex multiplier 507 that complexes a complex carrier and transitions to two baseband signals, and generates a sample corresponding to twice the symbol frequency from the output signal of the complex multiplier 507 and recovers the signal with a previously transmitted character. For adjusting the gain of the resampler 508 and the matched filter unit 509 and the baseband signal output from the matched filter unit 509 to match the filter used to transmit the input signal. It consists of multiplying the multiplier 510.

In this case, when the pass band signal is used by the pass band / base band data selector 503, the gain control loop is shortened and AGC can converge quickly. However, when the pass band signal is not passed through the band filter, a DC component and a noise component are present. Some pretreatment is required.

Conversely, choosing a baseband receive signal lengthens the gain control loop, reducing the convergence rate, but can lead to accurate errors.

The detailed configuration of the internal AGC block and the signal processing with the neighboring blocks are as follows.

6 is a detailed block diagram of an internal AGC block for removing AM Hum in the digital domain.

First, a signal selected by the passband / baseband data selector 620 includes a squarer 601 that squares an input signal and a subtractor 602 that obtains a difference between a power value of a squared received signal and a reference power value. And a gain error detector that obtains a gain error value by receiving an AGC power reference, and an LSHIFT register 611 that adjusts a bandwidth of a feedback loop by an AGC step signal when the gain error value is input, and a bandwidth is adjusted. The loop filter 610 including an adder 612 and a delay element (D flip-flop) 613 for accumulating the obtained gain error value, and the accumulated gain error value output from the loop filter 610 are multiplied by a pass band signal. In the digital domain, a multiplier 603 for outputting a corrected value and a delay element (D flip-flop) 604 for delaying an output signal of the multiplier 603 and feeding it back to the pass band / base band data selector 620 are provided. AM Hum This removes the internal AGC block is configured.

The MUX 630 selects the corrected pass band signal and the pass band signal by the internal AGC bypass signal, and the delay element 640 delay-outputs the signal selected by the MUX 630.

Here, the MUX 630 is a block for determining whether to bypass the pass band signal or to pass through the internal AGC block.

The inner AGC block is driven when it is unlocked by the AGC LOCK detector. In this case, the loop gain is controlled by the AGC step signal generated by the AGC LOCK detector, or the loop gain is fixed (FREEZE).

The automatic gain control device of the digital TV receiver according to the present invention has a phenomenon in which the gain fluctuates due to the noise generated by the power noise and other equipments generated when the AC power is switched to DC. To be removed within the digital domain.

In the automatic gain control apparatus of the present invention, the gain control of the external devices as well as the gain control of the external devices by selectively using a pass band signal or a base band signal while controlling the gain of the external devices at the time of AM Hum generation. Gain control is performed within the digital block, allowing for more stable removal of AM Hum.

In addition, in the case of using the passband reception signal, AM Hum can be quickly removed, and the baseband reception signal can be used to selectively extract the error although the convergence speed is relatively low.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the examples, but should be defined by the claims.

 The automatic gain control apparatus of the digital TV receiver of the present invention as described above has the following effects.

First, since the automatic gain control is performed in the digital block inside the chip by selectively using the passband reception signal or the baseband reception signal while controlling the gain of the external devices, it is possible to secure stability of AM Hum removal.

That is, it is possible to ensure the stability of AM Hum removal by performing AGC in the digital domain as well as the analog domain.

Second, the AM Hum can be quickly removed when using the passband reception signal, and the convergence rate is relatively slow but accurate error can be derived when the baseband reception signal is used. Applicability can be improved at the time.

Third, the AGC LOCK detector bypasses the internal AGC block or performs the freeze control, enabling optimal AGC and controlling the block inside the chip to facilitate chipping.

Claims (5)

A pass band / base band data selection unit for selecting an input pass band signal or a feedback base band signal; RF AGC control signal and IF AGC control for detecting gain error value by the power value of the input signal digitally converted and the DC component is removed and the set reference signal Pb_ref, and controlling the external gain by the AGC step signal An external AGC unit for outputting a signal; An internal AGC unit driven by the AGC step signal to control gain in the receiver using a signal selected by a pass band / base band data selection unit; And an AGC lock detector for detecting the convergence time of the automatic gain control loop using the AGC gain error output from the external AGC unit and generating an AGC step signal to control the loop gain of the automatic gain control loop. TV gain automatic gain control device. The method of claim 1, A Hilbert transducer separating the phase of a signal whose gain is controlled in the receiver by the internal AGC unit; A complex multiplier for complex multiplying the phase-separated signal with a complex carrier proportional to a phase error to transition to two baseband signals; Further comprising a resampler and a matched filter unit for generating a sample corresponding to twice the symbol frequency in the output signal of the complex multiplier and filtering to recover the signal to a previously transmitted character, And a feed back to the passband / baseband data selector through the multiplier to multiply the value for matching the gain of the baseband signal output from the matched filter unit. The method of claim 1, The internal AGC unit, A gain error detection unit configured to obtain a gain error value by using a subtractor for calculating a difference between a square of an input signal and a power value of the squared received signal and a reference power value; A loop filter comprising an LSHIFT register for adjusting the bandwidth of the feedback loop by an AGC step signal when the gain error value is input, an adder for accumulating the bandwidth-adjusted gain error value, and a delay element; A multiplier for multiplying a pass band signal by a cumulative gain error value output from the loop filter and outputting a corrected value, and a delay element for delaying an output signal of the multiplier and feeding it back to a pass band / base band data selector. Automatic gain control device of a digital TV receiver, characterized by removing the AM Hum. The method of claim 1, And a MUX for selecting a corrected passband signal and a passband signal by an internal AGC bypass signal to determine whether to bypass the passband signal or to pass through the internal AGC unit. Automatic gain control device. delete

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