The present invention relates to a filter device for processing input signals, in particular I[ntermediate]F[requency] input signals, for example sound signals, such as received television signals.
The present invention further relates to an electric or electronic circuit arrangement, in particular to a sound processing path, comprising
The present invention further relates to a method for processing input signals, in particular I[ntermediate]F[requency] input signals, for example sound signals, such as received television signals.
T[ele]V[ision] transmission is performed in multi channels, which can be adjacent (for example for cable transmission). For reception the desired channel has to be separated from the undesired adjacent channels (so-called channel selectivity). Furthermore for demodulation single carriers have to be separated from other carriers within the desired channel (so-called carrier selectivity).
In older concepts the selectivity of carriers is mainly done by external S[urface]A[coustic]W[ave] filters (reference numeral FIL in
The whole (analog) TV signal SIN is amplified by an amplifier AMP and fed to an I[nphase/]Q[uadrature] mixer IQM. This mixer IQM
As also shown in
Since the selectivity of carriers is mainly done by the external S[urface]A[coustic]W[ave] filter FIL a large variety of SAW filters is necessary for multistandard application in the prior art (low pass filter selectivity or real band pass filter selectivity with reference numeral RBS; cf.
Known current concepts for multistandard T[ele]V[ision] signal reception try to reduce the number of needed surface acoustic wave filters. To cover all possible TV standards including digital TV, two window SAW filters are used, one comprising a bandwidth of six M[ega]H[ert]z, and the other comprising a bandwidth of eight M[ega]H[ert]z.
However, in these prior art concepts image rejection with partly high requirements is needed to suppress adjacent channels; in this context, the channel selectivity is tried to be done by integration as much as possible.
Looking for analog TV sound processing in such prior art concepts shows that the second sound intermediate frequency carriers of the TV signal are surrounded
All frequency components are undesired and disturb the sound demodulation performance. A bandpass function around the desired sound carriers at TV standard dependent frequencies is necessary.
In this context, the basic principle of tuning and frequency switching of filters is known; also the basic principle of complex filtering or polyphase filtering is disclosed in prior art document U.S. Pat. No. 6,377,315 B1 referring to a polyphase filter output fed to a bandpass filter.
In this prior art document U.S. Pat. No. 6,377,315 B1, a polyphase circuit stage is used as a (supposedly passive) polyphase filter so as to provide image rejection. Besides, two real band pass filters are provided wherein one of these band pass filters is assigned to the I[nphase] path and the other of these band pass filters is assigned to the Q[uadrature] path. However, an active controlled polyphase filter is not revealed.
In the prior art article “A 900-MHz Dual-Conversion Low-IF GSM Receiver in 0.35-μm CMOS” by Shahrzad Tadjpour et al., IEEE Journal Of Solid State Circuits, Vol. 36, No. 12, December 2001, a system referring to the technological background of the present invention and being provided with two cascaded polyphase filters (=a passive polyphase filter and an active polyphase filter) with mixers and amplifiers is disclosed; between these two polyphase filters, the frequency situation is changed once by mixing; the passive polyphase filter provides the image rejection for the subsequent mixing, the active polyphase filter is switchable.
In prior art document U.S. Pat. No. 6,236,847 B1, two passive polyphase filters are used in tandem for achieving adjacent selectivity and image rejection; by this prior art document U.S. Pat. No. 6,236,847 B1, the technique of passive polyphase filtering is presented wherein two passive polyphase filters respectively suppress the negative frequency range; frequency mixing is necessary between these two passive polyphase filters in order to maintain a band pass characteristic; the resulting passing range is dependent on the input frequency. Since more than one channel passes there is no narrow-band channel selectivity and especially no carrier selectivity.
Starting from the disadvantages and shortcomings as described above and taking the prior art as discussed into account, an object of the present invention is to further develop a filter device of the kind as described in the technical field, a circuit arrangement of the kind as described in the technical field as well as a method of the kind as described in the technical field in such way that a bandpass function around the desired carriers is provided and that the sound demodulation performance is not disturbed.
The object of the present invention is achieved by a filter device comprising the features of claim 1, by a circuit arrangement comprising the features of claim 5 as well as by a method comprising the features of claim 8. Advantageous embodiments and expedient improvements of the present invention are disclosed in the respective dependent claims.
The present invention is principally based on the idea of combining at least two polyphase filters for integrated channel and carrier selectivity wherein
In this context, the at least one passive polyphase filter stage is designed for image rejection, and the at least one active polyphase filter stage is designed for band pass as well as for contributing to the image rejection in order to relax the attenuation requirements of the passive polyphase filter stage.
Thus, the active polyphase filter facilitates and/or supports the I[mage]R[ejection] specification of the passive polyphase filter (without this facilitation and/or support, the I[mage]R[ejection] would have to be realized solely by the passive polyphase filter); in other words, the active polyphase filter stage additionally provides image rejection.
By utilizing polyphase filtering, an optimal signal-to-noise ratio is obtained; negative frequencies do not contribute noise.
According to a preferred embodiment of the present invention, the at least one passive polyphase filter and the at least one active polyphase filter, the latter filter in particular being embodied as at least one active polyphase band pass filter, are cascaded in such way
According to an expedient embodiment of the present invention, the active polyphase band pass filter is designed
Regarding the advantages of the present invention, there is small integration effort by splitting the needed image rejection requirement into two (or more) filters, namely into
By the implementation according to the present invention, the application effort (four external ceramic band pass filters) is reduced by integrating one (or more) standard dependent switched filter; independently thereof or in connection therewith, only a small area is required for the integration by a standard dependent switched and tuned integrated band pass filter.
Using the present invention allows an equal band pass characteristic over a large frequency range whereas a real band pass would change the steepness of the sidewalls by tuning the frequency.
According to the method of the present invention, input signals, in particular l[ntermediate]F[requency] input signals, for example sound signals, such as received television signals, are processed by
said active polyphase filter stage being combined, in particular cascaded, with said passive polyphase filter stage.
Moreover, according to a preferred embodiment of the method according to the present invention,
The present invention can be used for channel selectivity and especially for sound processing in any analog I[ntegrated]C[ircuit] for T[ele]V[ision] signal handling including I[ntermediate]F[requency] processing with I[nphase/]Q[uadrature] mixing or internal generating I[nphase/]Q[uadrature] signals; the present invention can for example be used in an alignment-free multistandard (P[hase]A[lternating]L[ine], SE[quentiel]C[ouleur]A[vec]M[émoire], and N[ational]T[elevision]S[tandards]C[ommittee]) vision and sound l[ntermediate]F[requency] signal P[hase-]L[ocked]L[oop] demodulator for positive and negative modulation, including sound A[mplitude]M[odulation] and F[requency]M[odulation] processing.
The present invention finally relates to the use of at least one filter device as described above and/or of at least one circuit arrangement as described above and/or of the method as described above in at least one semiconductor-based audio tuner and/or video tuner signal application, for example in at least one integrated R[adio]F[requency] signal processing front end module, such as in at least one computer monitor, in at least one P[ersonal]C[computer], in at least one S[et-]T[op-]IB[ox], in at least one T[ele]V[ision] set, in at least one V[ideo]C[assette]R[ecorder] and/or in at least one V[ideo]T[ape]R[ecorder].
As already discussed above, there are several options to embody as well as to improve the teaching of the present invention in an advantageous manner. To this aim, reference is made to the claims respectively dependent on claim 1, on claim 5 and on claim 8; further improvements, features and advantages of the present invention are explained below in more detail with reference to a preferred embodiment by way of example and to the accompanying drawings where
The same reference numerals are used for corresponding parts in
As discussed above, known current T[ele]V[ision] I[nterrnediate]F[requency] concepts reduce the external selectivity of various S[urface]A[coustic]W[ave] filters with specific characteristic to the use of window SAW filters with two different bandwidths. The depicted new proposal replaces the leak in selectivity by the combination of a passive polyphase filter 50 for image rejection, i.e. providing the image rejection selectivity SIR (cf.
In other words, for improved channel selectivity and easier realization, smaller area, easier application, optimal signal-to-noise ratio and even performance over a large frequency range, for instance, for analog sound processing in TV receivers, the passive polyphase filter 50 and the active tuned polyphase bandpass filter 60 are cascaded.
In more detail,
The whole (analog) TV signal SIN is amplified by an amplifier 20 and fed to an I[nphase/]Q[uadrature] mixer 30. This mixer 30
As shown in
Like a real band pass, the poly phase band pass 60 attenuates the picture signals of the received channel P[icture]C[arrier], C[olour]C[arrier] and the lower adjacent channel signals, especially the picture carrier PCN-1. But furthermore the poly phase band pass 60 gives full contribution to image suppression, i.e. the required image suppression z[dB] is shared
In order to handle the process spread, the temperature dependency and the voltage dependency and so as to reach a high frequency accuracy for the band pass, the active polyphase band pass filter 60 is tuned by a control loop 200 as shown in
In other words, the polyphase bandpass filter 60 is a tuned filter in order to reduce the effects of the process spread, the temperature dependency and the voltage dependency with a control loop 200 as in
In more detail,
This control voltage CVO is used to tune the reference filter 70 to the desired frequency for which it shifts the phase of the reference signal SREF in the way that the control loop 200 is in steady state. The control voltage CVO is additionally used to control the polyphase bandpass filter 60, which matches to the reference filter 70.
For switching the band pass to various carrier frequencies the polyphase bandpass filter 60 gets a standard switch input signal SSS effecting the internal impedance level and thereby changing the filter mid frequency.
Number | Date | Country | Kind |
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05102214.3 | Mar 2005 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2006/050842 | 3/20/2006 | WO | 00 | 8/14/2008 |