WO2006011083A2

WO2006011083A2 - Consumer device comprising a signal converter

Info

Publication number: WO2006011083A2
Application number: PCT/IB2005/052301
Authority: WO
Inventors: Andrea Scenini
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-07-22
Filing date: 2005-07-12
Publication date: 2006-02-02
Also published as: JP2008507878A; WO2006011083A3; EP1776766A2; KR20070035099A; CN101023584A

Abstract

Consumer devices (1,11) comprise signal converters (2,12) for converting input signals into output signals. These signal converters (2,12) comprise chaotic dither generators (3,13,23,33) to reduce or attenuate pattern noise or idle tones resulting from input signals being slowly varying signals or having small amplitudes or comprising DC components. Chaotic dither generators (3,13,23,33) generate chaotic dither signals which decorrelate pattern noise or idle tones sufficiently, and better than pseudo random dither generators which generate dither signals based on finite pseudo random sequences. The signal converters (2,12) constitute oversampling converters or sigma delta modulators or delta sigma modulators. The chaotic dither generators (3,13,23,33) comprise transistor circuits (34) and amplifier (35) coupled to each other via switches (36,37). The transistor circuit (34) comprises three transistors (41-43). The signal converters (2,12) are low cost and low complex and have good price/performance ratios.

Description

Consumer device comprising a signal converter

The invention relates to a consumer device comprising a signal converter, and also relates to a signal converter for use in a consumer device, and to a method for converting signals in a consumer device, and to a processor program product for converting signals in a consumer device.

Examples of such a consumer device are HiFi systems, CD players/recorders, MP3 players/recorders, wired and/or wireless and/or mobile telephones, televisions, video players/recorders, DVD players/recorders and computers.

A prior art consumer device is known from US 6,326,911, which discloses a signal converter in the form of a delta-sigma modulator for converting an input signal into an output signal. In case of this input signal being a slowly varying signal or having a small amplitude or comprising a DC component, the output signal will comprise noise known as pattern noise or idle tones. To reduce or attenuate such pattern noise or idle tones, a dither generator is used. This dither generator comprises a pseudo random number generator coupled to a digital-to-analog converter, and generates a dither signal which is added to (a derivation of) the input signal. This dither signal decorrelates the pattern noise or idle tones. As a result, the pattern noise or idle tones are attenuated or reduced.

The known consumer device is disadvantageous, inter alia, owing to the fact that the dither generator generates a dither signal based on a pseudo random sequence. To keep the signal converter low cost, the pseudo random sequence will be relatively short. As a result, the noise pattern or idle tones are decorrelated insufficiently.

It is an object of the invention, inter alia, to provide a consumer device comprising a low cost signal converter in which the idle tones are decorrelated sufficiently. Furthers objects of the invention are, inter alia, to provide a low cost signal converter for use in a consumer device, a method for converting signals in a consumer device, and a processor program product for converting signals in a consumer device, in which the idle tones are decorrelated sufficiently. The consumer device according to the invention comprises a signal converter for converting an input signal into an output signal, which signal converter comprises a chaotic dither generator for generating a chaotic dither signal for reducing idle tones in the output signal. By introducing a chaotic dither generator, a dither signal is generated which is no longer based on a pseudo random sequence. As a result, the noise pattern or idle tones are decorrelated sufficiently. The consumer device according to the invention is further advantageous in that the signal converter has a good price/performance ratio.

A chaotic dither generator for example comprises a relatively large resistor coupled to a high-gain high-bandwidth amplifier for amplifying the thermal noise of the relatively large resistor.

It should be noted that US 6,404,260 discloses in its Figure 7 a chaotic circuit for generating a chaotic dither signal for dithering a clock signal. This is done to reduce the size of spikes of electromagnetic radiation generated by a circuit that uses this clock signal. Therefore, US 6,404,260 is related to protecting (performances of) other devices in the near environment. The invention is related to improving the performance of the consumer device itself and is not related to dithering clock signals.

An embodiment of the consumer device according to the invention is defined by the signal converter constituting an oversampling converter. Especially in oversampling converters, the dither generator is of high importance.

An embodiment of the consumer device according to the invention is defined by the signal converter constituting a sigma delta modulator or a delta sigma modulator. Especially in sigma delta modulators or a delta sigma modulators, the dither generator is of high importance. An embodiment of the consumer device according to the invention is defined by the signal converter further comprising a loop filter, a combiner and a quantizer, an output of the loop filter being coupled to a first input of the combiner, an output of the chaotic dither generator being coupled to a second input of the combiner, and an output of the combiner being coupled to an input of the quantizer. The combiner for example comprises an adder. Such an adder is a low cost circuit for adding a dither signal to (a derivation of) an input signal.

An embodiment of the consumer device according to the invention is defined by the loop filter being an analog loop filter, the combiner being an analog combiner, and the chaotic dither generator being coupled to the analog combiner via an interface. In this analog solution, the interface for example comprises voltage controlled current sources for converting voltage signals originating from the chaotic dither generator into currents destined for the combiner.

An embodiment of the consumer device according to the invention is defined by the loop filter being a digital loop filter, the combiner being a digital combiner, and an output of the quantizer being fed back to an input of the loop filter via a feedback circuit. This is a digital solution.

An embodiment of the consumer device according to the invention is defined by the chaotic dither generator comprising a transistor circuit and an amplifier, an output of the transistor circuit being coupled via a first switch to an input of the amplifier and an output of the amplifier being coupled via a second switch to an input of the transistor circuit. Compared to the chaotic dither generator consisting of the relatively large resistor coupled to the high-gain high-amplification amplifier, this chaotic dither generator comprising the transistor circuit and the amplifier will have a lower power consumption and will be less expensive owing to the fact that the amplifier does not need to be a high-gain high-bandwidth amplifier.

An embodiment of the consumer device according to the invention is defined by the chaotic dither generator further comprising a first capacitor coupled to the input of the transistor circuit and a first reference terminal and a second capacitor coupled to the input of the amplifier and a second reference terminal. Both capacitors have storage functions.

An embodiment of the consumer device according to the invention is defined by the transistor circuit comprising a first transistor comprising a control electrode constituting the input of the transistor circuit and coupled to a control electrode of a second transistor, a first main electrode of the second transistor being coupled to a third reference terminal and a second main electrode of the second transistor constituting the output of the transistor circuit and being coupled to a first main electrode of the first transistor, a second main electrode of the first transistor being coupled to a fourth reference terminal, which fourth reference terminal is further coupled to a first main electrode of a third transistor, a second main electrode of the third transistor being coupled to the second main electrode of the second transistor, and a control electrode of the third transistor constituting a biasing input of the transistor circuit. This chaotic dither generator is of a low complexity and therefore extremely low cost. The signal converter according to the invention for use in a consumer device for converting an input signal into an output signal is defined by comprising a chaotic dither generator for generating a chaotic dither signal for reducing idle tones in the output signal.

The method according to the invention for converting an input signal into an output signal in a consumer device is defined by comprising the step of generating a chaotic dither signal for reducing idle tones in the output signal.

The processor program product according to the invention for converting an input signal into an output signal in a consumer device is defined by comprising the function of generating a chaotic dither signal for reducing idle tones in the output signal. Embodiments of the signal converter according to the invention and of the method according to the invention and of the processor program product according to the invention correspond with the embodiments of the consumer device according to the invention, whereby a filter corresponds with a filtering step/function, a combiner corresponds with a combining step/function and a quantizer corresponds with a quantizing step/function etc. • ^{■ ■} The invention is based upon an insight, inter alia, that dither signals based on pseudo random sequences decorrelate idle tones insufficiently, unless the pseudo random sequences are sufficiently long, which makes the signal converter expensive, and is based upon a basic idea, inter alia, that a chaotic dither generator for generating a chaotic dither signal for reducing idle tones in the output signal is to be used. The invention solves the problem, inter alia, to provide a consumer device comprising a low cost signal converter in which the idle tones are decorrelated sufficiently, and is advantageous, inter alia, in that this signal converter has a good price/performance ratio.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments(s) described hereinafter.

In the drawings:

Fig. 1 shows diagrammatically a first embodiment of a consumer device according to the invention comprising a signal converter according to the invention;

Fig. 2 shows diagrammatically a second embodiment of a consumer device according to the invention comprising a signal converter according to the invention;

Fig. 3 shows diagrammatically a first embodiment of a chaotic dither generator;

Fig 4 shows diagrammatically a second embodiment of a chaotic dither generator;

Fig. 5 shows a non-linear input-output characteristic of a transistor circuit for the dither generator shown in Fig. 4; and Fig. 6 shows diagrammatically the transistor circuit for the dither generator shown in Fig. 4.

The consumer device 1 according to the invention shown in Fig. 1 comprises a signal converter 2 for converting an input signal into an output signal, which signal converter 2 comprises a chaotic dither generator 3 for generating a chaotic dither signal for reducing idle tones in the output signal. The signal converter 2 for example constitutes an oversampling converter. The signal converter 2 further comprises an analog loop filter 4, an analog combiner 5,6 and an analog quantizer 7. An output of the analog loop filter 4 is coupled to a first input of the analog combiner 5,6, an output of the chaotic dither generator 3 is coupled to a second input of the analog combiner 5,6 via an interafce 8, and an output of the analog combiner 5,6 is coupled to an input of the analog quantizer 7. Because of the analog loop filter 4 and the analog quantizer 7 being operated in a differential mode, the output of the analog loop filter 4 comprises two sub-outputs, the input of the analog quantizer 7 comprises two sub-inputs, and the analog combiner 5,6 comprises two analog adders 5 and 6, each one having a first sub- input which first sub- inputs together constitute the first input of the combiner 5,6 and each one having a second sub- input which second sub-inputs together constitute the second input of the combiner. The interface 8 couples an output of the chaotic dither generator 3 to the second sub-inputs of the analog adders 5 and 6. The interface 8 for example comprises voltage controlled current sources for converting voltage signals originating from the chaotic dither generator 3 into currents destined for the combiner 5,6.

The consumer device 11 according to the invention shown in Fig. 2 comprises a signal converter 12 for converting an input signal into an output signal, which signal converter 12 comprises a chaotic dither generator 13 for generating a chaotic dither signal for reducing idle tones in the output signal. The signal converter 12 for example constitutes a sigma delta modulator or a delta sigma modulator. The signal converter 12 further comprises a digital loop filter 14, a digital combiner 15 and a digital quantizer 17. An output of the digital loop filter 14 is coupled to a first input of the digital combiner 15, an output of the chaotic dither generator 13 is coupled to a second input of the digital combiner 15, and an output of the digital combiner 15 is coupled to an input of the digital quantizer 17. The digital combiner 15 comprises a digital adder. The digital quantizer is fed back to a first input of a digital adder 16 via a feedback circuit 18. A second input of this digital adder 16 forms the input of the signal converter 12, and an output of the digital adder 16 is coupled to an input of the loop filter 14.

In case of the input signal being a slowly varying signal or having a small amplitude or comprising a DC component, the output signal will comprise noise known as pattern noise or idle tones. To reduce or attenuate such pattern noise or idle tones, the chaotic dither generator 3,13 is used. This chaotic dither generator 3,13 generates a dither signal which is added to (a derivation of) the input signal. This dither signal decorrelates the pattern noise or idle tones. As a result, the pattern noise or idle tones are attenuated or reduced.

The chaotic dither generator 23 shown in Fig. 3 comprises a relatively large resistor 24 coupled to ground and to an input of a high-gain high-bandwidth amplifier 25. An output of this high-gain high-bandwidth amplifier 25 is coupled to a (positive or non-inverting) input of an amplifier 26, a (negative or inverting) input of this amplifier 26 is coupled to ground. The amplifier 26 receives a clock signal at its input 27 and generates a chaotic dither signal at its output 28. The chaotic dither generator 33 shown in Fig. 4 comprises a transistor circuit 34 and an amplifier 35, an output 45 of the transistor circuit 34 being coupled via a first switch 36 to an input of the amplifier 35 and an output of the amplifier 35 being coupled via a second switch 37 to an input 44 of the transisstor circuit 34. The chaotic dither generator 33 further comprises a first capacitor 38 coupled to the input 44 of the transistor circuit 34 and ground and a second capacitor 39 coupled to the input of the amplifier 35 and ground. Both capacitors have storage functions. At its output 40 corresponding with the input 44 of the transistor circuit 34, the chaotic dither generator 33 generates a chaotic dither signal. In Fig. 6, the transistor circuit 34 for the dither generator 33 shown in Fig. 4 comprises a first transistor 41 (NMOS) comprising a control electrode (gate) constituting the input 44 of the transistor circuit 34 and coupled to a control electrode (gate) of a second transistor 42 (NMOS). A first main electrode (source) of the second transistor 42 is coupled to ground and a second main electrode (drain) of the second transistor 42 constitutes the output 45 of the transistor circuit 34 and is coupled to a first main electrode (source) of the first transistor 41. A second main electrode (drain) of the first transistor 41 is coupled to a fourth reference terminal 47 constituting a supply voltage, which fourth reference terminal 47 is further coupled to a first main electrode (source) of a third transistor 43 (PMOS). A second main electrode (drain) of the third transistor 43 is coupled to the second main electrode (drain) of the second transistor 42. A control electrode (gate) of the third transistor 43 constitutes a biasing input 46 of the transistor circuit 34. Other kinds of transistors and transistor circuits are not to be excluded.

The non- linear input-output characteristic of the transistor circuit 34 for the dither generator 33 is shown in Fig. 5. By varying the voltage at the biasing input 46, the shape of the curve is changed.

The consumer device 1,11 according to the invention further comprises for example stages not shown. These stages comprise for example an input stage for example comprising a receiver for receiving signals and/or a source for generating signals, a signal processing stage for processing signals and comprising, inter alia, the signal converter 2,12 according to the invention, and an output stage for example comprising a transmitter for transmitting signals and/or an amplifier for amplifying signals and/or a reproducer for reproducing signals etc.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the consumer device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. Consumer device (1,11) comprising a signal converter (2,12) for converting an input signal into an output signal, which signal converter (2,12) comprises a chaotic dither generator (3,13,23,33) for generating a chaotic dither signal for reducing idle tones in the output signal.

2. Consumer device (1,11) according to claim 1, the signal converter (2,12) constituting an oversampling converter.

3. Consumer device (1,11) according to claim 1, the signal converter (2,12) constituting a sigma delta modulator or a delta sigma modulator.

4. Consumer device (1,11) according to claim 1, the signal converter (2,12) further comprising a loop filter (4,14), a combiner (5,6,15) and a quantizer (7,17), an output of the loop filter (4,14) being coupled to a first input of the combiner (5,6,15), an output of the chaotic dither generator (3,13) being coupled to a second input of the combiner (5,6,15), and an output of the combiner (5,6,15) being coupled to an input of the quantizer (7,17).

5. Consumer device (1,11) according to claim 4, the loop filter (4) being an analog loop filter, the combiner (5,6) being an analog combiner, and the chaotic dither generator (3) being coupled to the analog combiner (5,6) via an interface (8).

6. Consumer device (1,11) according to claim 4, the loop filter (14) being a digital loop filter, the combiner (15) being a digital combiner, and an output of the quantizer (17) being fed back to an input of the loop filter (14) via a feedback circuit (18).

7. Consumer device (1,11) according to claim 1, the chaotic dither generator (33) comprising a transistor circuit (34) and an amplifier (35), an output (45) of the transistor circuit (34) being coupled via a first switch (36) to an input of the amplifier (35) and an output of the amplifier (35) being coupled via a second switch (37) to an input (44) of the transisstor circuit (34).

8. Consumer device (1,11) according to claim 7, the chaotic dither generator (33) further comprising a first capacitor (38) coupled to the input (44) of the transistor circuit (34) and a first reference terminal (GND) and a second capacitor (39) coupled to the input of the amplifier (35) and a second reference terminal (GND).

9. Consumer device (1,11) according to claim 7, the transistor circuit (34) comprising a first transistor (41) comprising a control electrode constituting the input (44) of the transistor circuit (34) and coupled to a control electrode of a second transistor (42), a first main electrode of the second transistor (42) being coupled to a third reference terminal (GND) and a second main electrode of the second transistor (42) constituting the output (45) of the transistor circuit (34) and being coupled to a first main electrode of the first transistor (41), a second main electrode of the first transistor (41) being coupled to a fourth reference terminal (47), which fourth reference terminal (47) is further coupled to a first main electrode of a third transistor (43), a second main electrode of the third transistor (43) being coupled to the second main electrode of the second transistor (42), and a control electrode of the third transistor (43) constituting a biasing input (46) of the transistor circuit (34).

10. Signal converter (2,12) for use in a consumer device (1,11) for converting an input signal into an output signal, which signal converter (2,12) comprises a chaotic dither generator (3,13,23,33) for generating a chaotic dither signal for reducing idle tones in the output signal.

11. Method for converting an input signal into an output signal in a consumer device (1,11), which method comprises the step of generating a chaotic dither signal for reducing idle tones in the output signal.

12. Processor program product for converting an input signal into an output signal in a consumer device (1,11), which processor program product comprises the function of generating a chaotic dither signal for reducing idle tones in the output signal.