WO2005041405A1

WO2005041405A1 - Split band amplifier

Info

Publication number: WO2005041405A1
Application number: PCT/IB2004/052156
Authority: WO
Inventors: Marcel H. W. Van De Westerlo
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2003-10-27
Filing date: 2004-10-20
Publication date: 2005-05-06
Also published as: TW200525879A

Abstract

An amplifier for amplifying a broadband input signal (IN) comprises signal splitting means (20) for splitting the input signal (IN) into at least two sub-signals (s'1, s'2, s'3, s'4). The amplifier further comprises signal amplification means (40) for amplifying each one of the at least two sub-signals (s'1, s'2, s'3, s'4) and signal merging means (60) for merging the at least two amplified signals (s'l, s'2, s'3, s'4). By merging the at least two amplified signals (s'1, s'2, s'3, s'4) the amplified broadband input signal (OUT) is obtained having a minimized 2nd order distortion.

Description

Split band amplifier

The invention relates to an amplifier for amplifying a broadband input signal and also to a broadband amplification system comprising such an amplifier. The invention further relates to a method for amplifying a broadband input signal. The invention can be used in wireline communication systems in general and in broadband wireline communication systems in particular such as CATV or xDSL systems. Broadband signals typically have a frequency range that spans several octaves. A CATV signal for example, may have a frequency range of 5 octaves (40-870 MHz). Amplification of such a signal requires that the 2" order distortion of the amplifier is adequately suppressed in order to meet the functional requirements of such system.

A broadband amplifier of such kind is known from EP 0 920 125 A. Shown is an amplifier that suppresses the 2^nd order distortion by means of using a pair of transformers, one at the input and one at the output of the amplifier. Transformers however, a rather large which hampers an efficient integration and miniaturization of the amplifiers. Furthermore, since transformers are typically man-made on for example a ferrite core, the gain response and 2^nd order distortion suppression is not always constant which is disadvantageous.

It is therefore an object of the present invention to provide an improved amplifier that is arranged to suppress 2^nd order distortion without using a transformer. To this end, the amplifier is comprising: signal splitting means for splitting the input signal into at least two sub- signals; - signal amplification means for amplifying each one of the at least two sub- signals; signal merging means for merging the at least two amplified sub-signals so as to obtain an amplified broadband input signal having a minimized 2^nd order distortion. The invention is based upon the insight that the amount of 2^nd order distortion is proportional to the frequency range of the broadband input signal that is expressed in octaves. According to the invention the input signal is splitted up (segmentized) into sub- signals. Each of these sub-signals is having a frequency range that is smaller than the original broadband input signal. Therefore, each one of these sub-signals can be amplified with less 2"^d order distortion than the broadband input signal itself. By merging the amplified sub- signals, a broadband signal is obtained that corresponds with the amplified input signal but exhibits less 2" ^l order distortion than otherwise would be achievable, in addition, since the broadband input signal is amplified by the amplification of the sub-signals, less complex and thus less expensive amplifiers can be used. In another embodiment according to the present invention at least one of the at least two sub-signals is having a frequency range of one octave or less. This embodiment is based upon the insight that signals having a frequency range of one octave or less can be amplified without 2^nd order distortion. In an embodiment according to the present invention, the signal splitting means comprises at least an input filter for splitting the signal up into the at least two signals. Use of filters is a convenient way to split the signal since the passband of the filters determines the frequency range of the at least two signals. In addition, filters can be designed in such a way that they provide an impedance that corresponds with a required characteristic impedance. In an embodiment according to the present invention, the signal merging means comprises at least an output filter for merging the each of the at least two amplified signals. Use of filters offers a convenient way of merging the amplified sub-signals. In the first place because they effectively prevent backwards intermodulation of an amplified sub- signal to the output of other amplifiers, and secondly because they can be arranged to provide an impedance that corresponds to a required characteristic impedance. In an embodiment according to the present invention, the signal merging means are further arranged to delay at least one of the at least two amplified signals to assure that the amplified sub-signals are having an equal phase before they are merged in order to prevent phase errors in the amplified input signal. The delay means can constitute a delay line one could advantageously use the parasitic filter delay of the output filters. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. Fig. 1, shows a frequency spectrum of an input signal according to the present invention. Fig. 2, shows an example of a input filter section according to the present invention using bandpass filters. Fig. 3, shows an example of the passbands of an input filter arrangement according to the present invention. Fig. 4. shows another example of an input filter section according to the present invention using a cascaded filter. Fig. 5, shows an example of an implementation of an cascaded filter. Fig. 6, shows an embodiment of an amplifier according to the present invention using bandpass input and output filters. Fig. 7, shows another embodiment of an amplifier according to the present invention using cascaded input and output filters. Fig. 8, shows an example of an channel amplifier.

Fig. 1 shows by means of example the frequency spectrum 10 of a signal that ranges by means of example from 100 to 1100 MHz. Fig. 2 shows signal splitting means 20 comprising five bandpass input filters

21, 22,23,23 and 25 that are arranged to segmentize the broadband input signal into five sub- signals S1,S2,S3,S4 and S5. Each one of the sub signals S1,S2,S3,S4 and S5 is having a frequency band that is smaller than the frequency band of the original input signal IN. Fig. 3 shows the passbands 30,32,34,36 and 38 of the five (bandpass) input filters 21, 22,23,23 and 25. According to Fig. 3, the five bandpass filters 21,22,23,24,25 are having equal passbands. According to the present invention however, the bandpass filters 21,22,23,24,25 may also be designed to have different passbands. In an optimal configuration, the passbands of the filters 21,22,23,24 and 25 should not supersede one octave in order to avoid second order distortion. One octave corresponds for example, to passbands ranging from 100 to 200 MHz or from 200 to 400 MHz. Obviously, the second passband would yield a sub signal S1,S2,S3,S4 and S5 with a substantially larger bandwidth (200MHz) than the first passband (100 MHz). Evidently this phenomena can advantageously be exploited by those skilled in the art for obtaining an optimal amplifier. Fig. 4 shows an alternative embodiment of signal splitting means 20 comprising a cascade of low-pass filter 70,73 and high-pass filters 74 . The input signal IN is splitted into three sub-signals S'1,S'2,S'3. However, it will be apparent to those skilled in the art that the cascades can be extended further for splitting the input signal IN into more sub- signals if required. Fig. 5 shows a possible implementation of the cascaded filter, wherein the used filters are designed to comprise capacitors and coils only. Each one of the low-pass filters 70 and 73 comprise two coils L1,L2, L4,L5 and one capacitor Cl respectively C4. The high-pass filters 72 and 74 on the other hand comprise, two capacitors each C2,C3, C5,C6 and one coil L3,L6. The value of these components can easily be determined by those skilled in the art and will largely be determined by the required frequency ranges of sub -signals S'1,S'2,S'3. In addition those skilled in the art will be able to design the filter such that the filter at node A inhibits a characteristic impedance. Fig. 6 shows an example of a broadband amplifier according to the present invention. Shown are signal splitting means 20, signal amplification means 40 and signal merging means 60. The signal splitting means 20 may comprise five bandpass filters 21-25 having corresponding passbands 30,32,34,36 and 38. The passband filters split the input signal IN up into 5 sub-signals SI- S5. Each one of these 5 sub-signals S1-S5 is individually amplified by the amplification means 40. Amplification means 40 comprises conventional amplifiers 41, 42, 43,44,45. An example of such a conventional amplifier is shown in Fig. 8. Also shown are the signal merging means 60 comprising bandpass filters 61,62,63,64 and 65. Typically, these bandpass filters have a (parasitic) filter delay that according to the present invention is used to an advantage for matching the phases of the amplified sub-signals. Alternatively it would be possible to delay the sub-signals by means of delay lines (not shown here). In addition, bandpass filters are high-impedant outside their passbands which prevents backwards intermodulation of signals S"l, S"2,S"3, S"4 and S"5 . I.e. the amplified sub-signals S" 1, S"2,S"3, S"4 and S"5 can no longer influence the preceding amplifiers 41,41,43 and 44. It will be appreciated by those skilled in the art that this too will considerably improve amplifier performance. Besides, the input filters 21-25 and output filters 61-65 can be designed to have a characteristic impedance. Herewith, it is possible to couple the amplifier to a telecommunication system in a non-reflectional way. Fig. 7 shows an alternative implementation of the amplifier according to the present invention. By means of example, the amplifier is arranged to split the broadband input signal IN up into three sub-signals S'l, S'2 and S'3. According to this embodiment, the signals are splitted and merged through group of cascaded filters 70-74, 75-78. The signal splitting means comprise low-pass filters 70,73 and high-pass filters 72 and 74. The signal merging means are a mirror image of the signal splitting means. I.e. it comprises low-pass filters 77, 75 and high-pass filters 78 and 78. The cascaded filters can be extended further to accommodate a splitting of the broadband input signals into more sub-signals if required. In addition the cascaded filters can be designed to provide a required characteristic impedance. As was the case with Fig. 6, it possible to used the parasitic delay of the cascaded filters for matching the phase of the amplified sub signals. Likewise, it is possible to use delay lines for this purpose (not shown here). Fig. 8 shows an example of a channel amplifier 41,42,43,44,45. The amplifier comprises a transistor 50 that is having a back-coupling between collector c and base b. Emitter e is grounded if required thru a resistor (not shown here). It is to 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. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. 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

CLAIMS:

1. Amplifier for amplifying a broadband input signal (IN), the amplifier comprising: signal splitting means (20) for splitting the input signal (IN) into at least two sub-signals (s' ι,s'₂,s'₃,s'₄); - signal amplification means (40) for amplifying each one of the at least two sub-signals (s'ι,s'2,s'₃,s⁵4); signal merging means (60) for merging the at least two amplified signals (s"ι,s"₂,s"₃,s"₄) so as to obtain an amplified broadband input signal (OUT) having a minimized 2^nd order distortion.

2. Amplifier according to claim 1, wherein at least one of the at least two sub- signals (s'ι,s'₂,s'₃,s'₄) is having a frequency range of one octave or less.

3. Amplifier according to claims 1, wherein the signal splitting (20) means comprises at least an input filter (21-25, 70-74) for splitting the input signal (IN) up into the at least two sub-signals (s'ι,s'₂,s'₃,s'4).

4. Amplifier according to claims 1, wherein the signal merging(60) means cornprises at least an output filter (61-65, 75-78) for merging the each of the at least two amplified sub-signals (s"ι,s"₂,s"₃,s"₄).

5. Amplifier according to claim 1 or 4, wherein the signal merging (6) means are further arranged to delay at least one of the at least two amplified sub-signals(s"ι,s"₂,s"₃,s" ).

6. Amplifier according to claim 5, wherein at least one the at least two amplified sub-signals (s"ι,s"₂,s"₃,s" ) is delayed by means of a filter delay of the output filter (61-65, 75-78).

7. Amplifier according to claims 1 or 5, wherein the signal merging means (60) comprises a signal delay line for delaying at least one of the at least two amplified sub- signals (s"_lss"_2>s"_3>s"₄).

8. A broadband signal amplification system comprising an amplifier according to one of the previous claims.

9. A method for amplifying a broadband input signal (IN), the method comprising the steps of: - splitting the input signal into at least two sub-signals(s' ι,s'₂,s'₃,s'₄); amplifying each one of the at least two sub-signals (s' ι,s'₂,s'₃,s'₄); merging the at least two amplified sub -signals (s"ι,s"₂,s"_3js" ) for obtaining an amplified broadband input signal (OUT) with minimized 2^nd order distortion.