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Bandwidth-adjustable filter

a filter and bandwidth technology, applied in the field of filters, can solve the problems of distorted signal constellation, increased bit error rate, and inability to meet the requirement of high accuracy for the wireless communication system, and achieve the effect of higher resolution

Active Publication Date: 2010-03-11
REALTEK SEMICON CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The solution provides a higher resolution for bandwidth adjustment, reducing bit error rates by allowing more accurate matching of 3 dB frequencies between I-channel and Q-channel signals, thus enhancing system stability.

Problems solved by technology

When the signals in the I-channel and in the Q-channel have a phase difference not equal to 90 degrees, the signal constellation is distorted and the bit error rate is thus increased.
In the modulation mechanism of FIG. 1, a capacitive array method is used to achieve the modulation of 3 dB frequency by adjusting the valid capacitance C. However, the conventional modulation mechanism has a minimum adjustable scale only about 2˜3%, which cannot meet the requirement of high accuracy for the wireless communication system.

Method used

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Embodiment Construction

[0018] Referring to FIG. 2, a circuit diagram of a bandwidth-adjustable filter according to a preferred embodiment of the invention is shown. The filter 200 includes an operational amplifier 210. The operational amplifier 210 has a negative input terminal and a positive input terminal coupled to the ground. The operational amplifier 210 is a single-input-terminal amplifier preferably. The filter 200 further includes a first adjustable resistor R1′, a first capacitor C1, a second capacitor C2, a second resistor R2 and a third resistor R3. The adjustable resistor R1′ has a first terminal defined as a node N1 and a second terminal defined as a node N2. The first terminal of the first adjustable resistor R1′ is coupled to the negative input terminal of the operational amplifier 210. The first capacitor C1 has a first terminal coupled to the node N1 and a second terminal coupled to the output terminal of the operational amplifier 210. The second capacitor C2 has a first terminal grounded...

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Abstract

A bandwidth-adjustable filter includes an operational amplifier, a first resistor, a first capacitor and a first resistor ladder circuit. The operational amplifier has a negative input terminal and a positive input terminal The first resistor is coupled to one of the input terminals of the operational amplifier. The first capacitor is coupled to the first resistor. The first resistor ladder circuit is coupled in parallel to the first resistor for changing the resistance of the first resistor so as to adjust the bandwidth of the filter.

Description

[0001] This application claims the benefit of Taiwan application Serial No. 94114457, filed May 4, 2005, and U.S. application Ser. No. 11 / 148,132, filed Jun. 9, 2005, the subject matter of which is incorporated herein by reference.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The invention relates in general to a filter, and more particularly to a bandwidth-adjustable filter. [0004] 2. Description of the Related Art [0005] In wireless communication systems, according to a common modulation mechanism, when in-phase signals (I-channel) and quadrature-phase signals (Q-channel) have different 3 dB bandwidth (ω0) in the filter, these two kinds of signals cannot match in phase. When the signals in the I-channel and in the Q-channel have a phase difference not equal to 90 degrees, the signal constellation is distorted and the bit error rate is thus increased. Therefore, in order to maintain system stability, it is very important that the filter has accurate 3dB bandwi...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): H03K5/00
CPCH03H11/1291H03H11/1286H03K5/086
Inventor LEE, CHAO-CHENGLIN, YING-YAO
Owner REALTEK SEMICON CORP