WO2007026259A2

WO2007026259A2 - Receiver for analog tv signals

Info

Publication number: WO2007026259A2
Application number: PCT/IB2006/003392
Authority: WO
Inventors: Khaled Maalej; Julien Schmitt
Original assignee: Dibcom
Priority date: 2005-08-04
Filing date: 2006-08-04
Publication date: 2007-03-08
Also published as: EP1913767A2; WO2007026259A3

Abstract

This receiver for an analog TV signal comprises a tuner (6) adapted to receive a radiofrequency signal corresponding to said analog TV signal and to directly output corresponding base band signals (I and Q) and an analog demodulator for analog TV signals (16) adapted to receive said base band signals (I and Q) and to combine these signals to deliver a demodulated analog TV signal.

Description

RECEIVER FOR ANALOG TV SIGNALS

The present invention concerns the reception of analog TV signals. The so called analog TV signals are analog signals carrying television information in an analog format by opposition to digital TV signals referring to analog signals carrying television information in a digital format. Generally, analog TV signals are received by a tuner delivering an

Intermediary Frequency signal, or IF signal. This IF signal is filtered by use of Surface Acoustic Waves filters, also called SAW filters, providing a filtered signal to an analog demodulator. The SAW filters are adapted to filter the signal depending upon its standard. For example, different SAW filters are used to process PAL and SECAM standard signals. Alternatively, one SAW filter is used to process several standards but with a lower quality.

The demodulator applies the relevant demodulation or equalization processing to derive the demodulated analog TV signal, also called final TV signal. Alternatively, the tuner has built-in filter and demodulator to deliver directly the final TV signals.

In any of these embodiments, the tuner and the demodulator are power consuming components and an overall power of 1 W to 1 ,5 W is required which is not suitable to certain applications, especially in handheld devices. Furthermore, the existing devices are set for one specific standard.

The component and the processing are designed to handle one type of signal and achieve low performances when used with other types of signal as indicated above.

This is the case for example in the device disclosed in the document US-A-4 974 086 in which the filters are set and the signal is converted to a fixed range of frequencies depending upon the filters.

Usually, customizable filters are used only with demodulators for digital signals as the demodulators for analog signals dictates strong constraints on the filters. The aim of the present invention is to solve this problem by providing a receiver for analog TV signals that reduces power consumption with an enhanced flexibility.

To this effect, the invention relates to a device as recited in claim 1. Thanks to this particular architecture using a tuner adapted to receive a radiofrequency signal and to deliver base band signals, also called Zero-IF tuner, in combination with an adapted analog demodulator and without SAW filter, the overall power consumption of the receiver is reduced, for example it is reduced by 1/5^th. Furthermore, the use of digital customizable filters allows more flexibility.

Other features and advantages of the invention will be apparent from the following description illustrated by the drawings in which:

- figure 1 is a block diagram of one embodiment of the invention; and - figure 2 is a block diagram of another embodiment of the invention.

In the first embodiment represented on figure 1 , the receiver 2 comprises an antenna 4 receiving radiofrequency (RF) signals and connected to a Zero-IF tuner 6. A so called Zero-IF tuner is adapted to receive signals at a radiofrequency and processed them to deliver directly base band signals. Such tuners are essentially used in receivers for digital TV signals and comprise two multipliers, each receiving the input RF signal and achieving frequency down conversions to deliver base band signals. In the example, tuner 6 receives the RF signal from the antenna 4 and delivers two base band signals respectively referred to as signals I and Q. Each of these two base band signals carries a part of the analog TV information.

In the embodiment described, the outputs of this tuner 6 are connected to a filter 8, such as a built-in filter or a separate component. This filter 8 is an analog Jrequen_cy_ dependant filter and is adapted to rejects so called adjacent channels by rejecting the components of the signal which are not in the desired range of frequency. Advantageously, it also comprises low consumption components.

In the described embodiment, the filter 8 is customizable and is provided with different sets of parameters depending upon the standard of the received signal. The customisation can be achieved by use of a hardware setting or by software. Advantageously, the customisation depends on the signal itself and a feedback information is generated after a scan of the entire frequency band. The Zero-IF tuner 6 then provides the base band signals to a demodulator 10 delivering the demodulated analog TV signal.

This demodulator 10 comprises first an analog to digital converter 12 for converting the two base band signals I and Q to deliver two corresponding digital signals which carry the analog TV information. Advantageously, the output signals are introduced in a Direct Digital

Synthesiser DDS 13 which allows moving the carrier of the signal along the frequency band. Thus it is possible to adapt the signal to the abilities of the downstream filters. In the embodiment described, the carrier of the video signal is moved to fit into the downstream filters frequency range. The signals are then fed to a compensation module 14 which compensates the frequency and gain mismatches introduced by the tuner 6.

In particular, the compensation module 14 corrects the phase and/or gain of the base band signals to compensate modifications introduced by the multipliers of the zero-IF tuner 6. This is achieved by the use of processing algorithms or any equivalent means in module 14. In case the modifications introduced by the tuner 6 are considered not to be relevant, the compensation module 14 can be dispensed with.

Finally, the two digital and compensated signals carrying analog TV information are fed to a demodulator element 16 for analog TV signals, also called analog demodulator element, although being a digital component. The signals provided to the analog demodulator element 16 are digital signals similar to base band signals I and Q in their electrical characteristics and the inputs of the analog demodulator element 16 are specially adapted to receive them. Furthermore, the analog demodulator element 16 is adapted to process these signals together and combine them to deliver the final analog TV signal. In the example, this combination comprises the processing in parallel of each of these two signals and their merging in order to extract the useful data.

Advantageously, the analog demodulator element 16 is connected to a digital customizable filter 18 which can be controlled to filter the signal depending upon its standard. For example, the filter is adapted to switch between different sets of parameters to achieving the filtering of a signal complying with different standards such as the PAL or the SECAM standard.

The use of the DDS 13 allows moving the signal into the filtering optimal frequency range. Thus, even if the filter 18 is set to match the demodulator constraints, the signal is moved along the frequency band to achieve an optimized filtering.

This particular architecture of the receiver with a Zero-IF tuner associated with an adapted analog demodulator element permits the use of low power consumption components.

Especially, this allows the use of silicon built-in components achieving the reception and demodulation of an analog TV signal with an overall power consumption of about 400 to 600 mW.

This particular architecture also permits to avoid the use of SAW filters between the tuner and the demodulator which are replaced by digital customizable filters. More precisely, the filter in the tuner rejects adjacent channels and the digital customizable filter assumes the standard dependant filtering. When a DDS is used, it also allows moving the signal within the optimal filtering range of frequencies. This offers flexibility to support different standards with the same components without the need to change SAW filters or have dual SAW filters. In the described embodiment, the filtering element 8, the converter element 12 and the compensation element 14 are built-in elements. In other embodiments, any or all of these components can be separated components.

Referring now to figure 2, another embodiment of the invention is described.

In this embodiment, the same tuner 6 with filter 8 is used in order to provide two base band signals to a demodulator 20 adapted to process both digital and analog TV signals by use of either the analog demodulator element

16 or a demodulator element for digital TV signals 22, also called digital demodulator element.

The receiver 2 also comprises a type detection unit 24 adapted to distinguish signals between analog TV signals and digital TV signals. In the example, this type detection is achieved by tracking the delivered demodulated signals during an initialization stage. A corresponding channel table is then memorized. Thus, once the channel table is determined, the identification of the received type of signal results from the identification of the received TV channel.

As described with reference to figure 1 , the two base band signals are fed to the analog to digital converters 12, to the DDS 13 and to the processing element 14.

In this embodiment, the processing element 14 also receives information from the type detection unit 24 indicating the signal type between an analog TV signal and a digital TV signal.

In both cases the processing element 14 achieves a compensation to correct the phase and /or the gain of the two signals base band signals to compensate the noise introduced by the tuner 6. The algorithms used to compare and level the signals can be the same or can be dependant upon the signal type.

If the received signal is identified as an analog TV signal, then the processed digital signals carrying analog TV information, as delivered by the processing element 24, are transferred to the analog_demodulator_ 16 which delivers the demodulated analog TV signal as described above with reference to figure 1.

If the received signal is identified as a digital TV signal, the I and Q signals corresponds to the complex and real part of the received signal and are transferred to the digital demodulation element 22 which delivers a demodulated digital TV signal in a conventional way.

Advantageously, the device also comprises a power management unit 26 which receives the information about the type of signal as detected by the type detection unit 24 in order to supply power to the required components i.e. to the components used to process the type of signal identified.

In the example, the power management unit 26 shuts down the analog demodulation element 16 when the received signal is a digital TV signal and oppositely shuts down the digital demodulator element 22 when the received signal is an analog TV signal. Thus, the signal type detection unit, trough the power management unit 26, controls the tuner to provide the base band signals to the corresponding demodulator depending upon the signal type.

The outputs of the analog demodulation element 16 and of the digital demodulator element 22 are connected to the digital customizable filter 18 which runs as described with reference to figure 1.

Accordingly, the architecture of this device is adapted to receive alternatively an analog TV signal and a digital TV signal by use of the same

Zero-IF tuner associated with an adapted analog demodulator element and a classical digital demodulator element, thus allowing the use of low power consumption components, of digital filters and avoiding the use of SAW filters.

Furthermore, by use of a power consumption management unit, the overall power consumption can be reduced.

Of course, many other embodiments are possible. Especially, another distribution of the elements can be achieved still with the same global architecture. For example in another embodiment, the analog to digital converters are included in the tuner which delivers directly digital base band signals.

Furthermore, the digital and analog demodulator elements described with reference to figure 2 can be on the same chip or on several chips. For example, the converters, the processing element and the digital demodulator element are on one chip, and the analog demodulator element is on another chip.

Yet in another embodiment the receiver as described with reference to figure 2 comprises a switch controlled by the type detection unit and connecting the output of the tuner 6 alternatively to an analog and digital demodulator depending upon the type of signal detected.

Alternatively, the type detection unit is implemented in software, for example in the demodulator software, which is then used to control the switch.

Such a receiver can be adapted in any kind of electronic articles such as digital television receivers, computers, laptops, handled devices or the like and the internal components thereof.

Claims

1. Receiver for an analog TV signal, characterized in that it comprises a tuner (6) adapted to receive a radiofrequency signal corresponding to said analog TV signal and to directly output corresponding base band signals (I and Q) to an analog frequency dependant filter (8) which outputs are connected to a demodulator for analog TV signals (16) adapted to receive said base band signals (I and Q) and to combine said base band signals to deliver a demodulated analog TV signal to at least one digital filter (18).

2. Receiver according to claim 1 , further comprising an analog to digital converter unit (12) connected between the tuner (6) and the demodulator for analog TV signals (16) to convert the base band signals (I and Q) delivered by said tuner (6) into corresponding digital signals provided to said demodulator for analog TV signals (16).

3. Receiver according to any of claims 1 and 2, further comprising a compensation unit (14) connected between said tuner (6) and said demodulator for analog TV signals (16), adapted to compensate the phase and/or gain noise of said base band signals.

4. Receiver according to any of claims 1 to 3, further comprising a demodulator for digital TV signals (22) provided with said base band signals to deliver a demodulated digital TV signal.

5. Receiver according to claim 4, further comprising a signal type detection unit (24) adapted to control the tuner (6) to provide said base band digital signals to the corresponding demodulator (16, 22) depending if the signal is identified as an analog TV signal or as a digital TV signal.

6. Receiver according to any of claims 4 and 5, further comprising a power management unit (26) adapted to supply power to the required components depending upon the type of signal received.

7. Receiver according to claim 6, wherein the power management unit

(26) is adapted to reduce the power supplied to the demodulator for digital TV signals (22) when the signal is identified as an analog TV signal and to reduce the power supplied to the demodulator for analog TV signals (16) when the signal is identified as a digital TV signal.

8. Receiver according to any of claims 1 to 7, wherein said at least one digital filter (18) is customizable and is provided with different sets of parameters depending upon the standard of the received signal.

9. Receiver according to any of claims 1 to 8, wherein said analog frequency dependant filter (8) is customizable and is provided with different sets of parameters depending upon the standard of the received signal.

10. Receiver according to any of claims 1 to 8, further comprising a DDS (13) connected between the tuner (6) and the demodulator for analog TV signals (16) to move the signal along the frequency band depending on the filtering abilities of the receiver.