Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Patent
1999-01-14
2000-09-12
Le, Dinh T.
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
327552, 327559, 330305, H03K 500
Patent
active
061183326
ABSTRACT:
In radio receivers, ceramic filters are used for filtering the received frequency band. The limitation of the frequency band in the higher frequency range leads to an asymmetrical crosstalk between the right and left audio channel after decoding in the stereo decoder. These transmission errors are compensated by an adjustable high-pass filter. This high-pass filter precedes the stereo decoder. High-pass filters using potentiometers cannot be integrated. Furthermore, ageing phenomena occur in potentiometers so that the transfer function changes. A high-pass filter with a variable capacitor can neither be integrated easily. Therefore, an arrangement is used in which, after a first amplification of the signal to be filtered, this signal is divided into two signal currents and the amplitude and phase of a sub-current are corrected. This corrected sub-current is added to the main current at a sum node. The sub-current is applied via a voltage divider unit to an amplifier stage having a plurality of inputs. A corresponding input, to which a partial voltage is assigned, is selected via a selection unit. The output of the amplifier stage supplies a changeable voltage which is present at the capacitor. By selecting the partial voltage, the transfer function of the high-pass filter can be adjusted. Transmission errors caused by the low-pass behavior of the ceramic filters are thereby reduced so that the stereo decoder receives a signal which can be accurately separated in the left and the right channel. This circuit arrangement can be integrated in that an adjustable capacitor is realized which consists of a voltage divider, an amplifier stage and the capacitor.
REFERENCES:
patent: 4509021 (1985-04-01), van Uden
patent: 5724006 (1998-03-01), Killian et al.
V. Riso "Miniturization of Filters" IBM Technical Disclosure Bulletin, vol. 12, No.-5 Oct. 1969, pp. 662-663.
Goodman Edward W.
Le Dinh T.
U.S. Philips Corporation
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