CN101777881A - Tracking filter with adjustable frequency bandwidth - Google Patents

Abstract

The invention discloses a tracking filter with adjustable frequency bandwidth, which comprises a first resistor, a first inductor, a first capacitor, a first MOS (metal oxide semiconductor) tube, a second MOS tube and a second capacitor, wherein one end of the first resistor is respectively connected with one end of the first inductor, one end of the first capacitor and the drain electrode of the first MOS tube; the other end of the first resistor is respectively connected with the other end of the first inductor, the other end of the first capacitor and the source electrode of the second MOS tube; the grid electrode of the first MOS tube is connected with the grid electrode of the second MOS tube; and the source electrode of the first MOS tube is connected with the second capacitor in series and then connected with the drain electrode of the second MOS tube. In the invention, a numerically controlled resistor is introduced, so that the bandwidth change of the tracking filter can be controlled to be less than a definite value in a wide frequency band.

Description

The tracking filter of bandwidth adjustable frequency

Technical field

The present invention relates to a kind of tracking filter of bandwidth adjustable frequency, belong to the technical field of tracking filter.

Background technology

Signal specific is in certain characteristic frequency or frequency range, and nearly all there is either large or small signal in all frequency ranges.Receive this signal specific, the interference of just necessary other frequency ranges of filtering.This just needs filter.Initial frequency-selecting function is realized by the filter of radio-frequency front-end.The RLC antiresonant circuit is a filter that quality factor is higher.

Simultaneously, in some applications, during for example television receiver was used, the useful signal channel was not fixed, and channel and TV station number are direct correlation.Function is television receiver completely, should be able to receive all TV stations that signal strength signal intensity surpasses system sensitivity.For another example, in radio communication, such as GSM, CDMA, WCDMA is in the system terminal mobile phones such as TD-SCDMA, mobile phone must cover tens and even the frequency range of hundreds of megahertz, and in reality conversation or wireless Internet access process, the link frequency range of base station and mobile phone has only hundreds of KHz or a few megahertz, and this link frequency range might real-time change (being frequency hopping).Therefore, fixed L C value is just infeasible.

Prior art: at TV domain, adopt the rough segmentation frequency range in the traditional boxlike tuner that constitutes by a large amount of discrete inductance electric capacity etc., cooperate voltage controlled capacitor to constitute the controlled tracking filter of resonance frequency, thereby adjust centre frequency, to satisfy the requirement of television reception.Along with development of integrated circuits, the tracking filter that can adjust resonance frequency has on a large scale been left and has integratedly been advanced in single chip or the several chip.Different with the voltage controlled capacitor that tradition adopts, be the integrated circuit of carrier with the chip, the mode of adjusting resonance frequency generally adopts the mode of numerical control electric capacity, promptly with the partition capacitance in switch access or the disconnection resonant cavity.In other words, adopted the technology of digital-to-analogue conversion, analog quantity is exactly a capacitance, thereby disperses.

Because it is big especially that some application bandwidth covers, if the fixed resistance value, the bandwidth of tracking filter will great changes will take place so.Resonance frequency is low more, and bandwidth is narrow more.Particularly for high frequency, bandwidth is too wide, effectively the filter bag external signal.

Summary of the invention

The present invention seeks to provide a kind of tracking filter of bandwidth adjustable frequency at the defective that prior art exists.

The present invention adopts following technical scheme for achieving the above object:

The tracking filter of bandwidth adjustable frequency of the present invention, comprise first resistance, first inductance and first electric capacity, it is characterized in that also comprising first, second metal-oxide-semiconductor and second electric capacity, wherein an end of first resistance connects an end of first inductance, an end of first electric capacity and the drain electrode of first metal-oxide-semiconductor respectively, the other end of first resistance connects the other end of first inductance, the other end of first electric capacity and the source electrode of second metal-oxide-semiconductor respectively, the grid of first metal-oxide-semiconductor connects the grid of second metal-oxide-semiconductor, and the source electrode of first metal-oxide-semiconductor is connected in series the drain electrode that connects second metal-oxide-semiconductor behind second electric capacity.

The tracking filter of bandwidth adjustable frequency, comprise first inductance and first electric capacity, it is characterized in that also comprising first to the 3rd metal-oxide-semiconductor, first resistance, the 3rd resistance and second electric capacity, wherein an end of first inductance connects an end of first electric capacity respectively, one end of the 3rd resistance, the drain electrode of the drain electrode of first metal-oxide-semiconductor and the 3rd metal-oxide-semiconductor, the other end of first inductance connects the other end of first electric capacity respectively, the other end of the 3rd resistance, one end of the source electrode of second metal-oxide-semiconductor and a resistance, the grid of first metal-oxide-semiconductor connects the grid of second metal-oxide-semiconductor, and the source electrode of first metal-oxide-semiconductor is connected in series the drain electrode that connects second metal-oxide-semiconductor behind second electric capacity.

The present invention has introduced digit-control resistance, makes in very wide frequency range, and the bandwidth change of controlling this tracking filter is less than certain value.

Description of drawings

Fig. 1: Second-Order RLC Filter Circuit parallel resonance filter;

Fig. 2: centre frequency digitally tunable filters;

Fig. 3: filter 1 of the present invention;

Fig. 4: filter 2 of the present invention.

Embodiment

Be elaborated below in conjunction with the technical scheme of accompanying drawing to invention:

As shown in Figure 1, Second-Order RLC Filter Circuit parallel resonance filter.

Centre frequency: $f=\frac{1}{2\mathrm{\π}\sqrt{\mathrm{LC}}};$

Bandwidth: $\mathrm{BW}=\frac{1}{2\mathrm{\πRC}}.$

As shown in Figure 2, the tracking filter of bandwidth adjustable frequency, comprise first resistance R 1, first inductance L 1 and first capacitor C 1, it is characterized in that also comprising first, the second metal-oxide-semiconductor M1, the M2 and second capacitor C 2, wherein an end of first resistance R 1 connects an end of first inductance L 1 respectively, one end of first capacitor C 1 and the drain electrode of the first metal-oxide-semiconductor M1, the other end of first resistance R 1 connects the other end of first inductance L 1 respectively, the source electrode of the other end of first capacitor C 1 and the second metal-oxide-semiconductor M2, the grid of the first metal-oxide-semiconductor M1 connects the grid of the second metal-oxide-semiconductor M2, and the source electrode of the first metal-oxide-semiconductor M1 is connected in series the drain electrode that meets the second metal-oxide-semiconductor M2 after second capacitor C 2.By changing inductance and electric capacity, can change the centre frequency of band pass filter: $\frac{1}{2\mathrm{\π}\sqrt{L(C_{\min }+\mathrm{dig}*C_{\mathrm{step}})}}\≤f\≤\frac{1}{2\mathrm{\π}\sqrt{{\mathrm{LC}}_{\min }}};$

Bandwidth: $\mathrm{BW}=\frac{1}{2\mathrm{\πR}(C_{\min }+\mathrm{dig}*C_{\mathrm{step}})}.$

Shortcoming, bandwidth change are too big.Particularly for high frequency, bandwidth is too wide, effectively the filter bag external signal.

As shown in Figure 3, the tracking filter of bandwidth adjustable frequency, comprise first inductance L 1 and first capacitor C 1, it is characterized in that also comprising first to fourth metal-oxide-semiconductor M1～M4, first to the second resistance R 1～R3 and second capacitor C 2, wherein an end of first inductance L 1 connects an end of first capacitor C 1 respectively, one end of the drain electrode of the first metal-oxide-semiconductor M1 and the 3rd resistance R 3, the other end of first inductance L 1 connects the other end of first capacitor C 1 respectively, the source electrode of the second metal-oxide-semiconductor M2, one end of the source electrode of the 4th metal-oxide-semiconductor M4 and second resistance R 2, the other end of the 3rd resistance R 3 connects the drain electrode of an end and the 3rd metal-oxide-semiconductor M3 of first resistance R 1 respectively, the other end of first resistance R 1 connects the other end of second resistance R 2 respectively, the source electrode of the 3rd metal-oxide-semiconductor M3, the drain electrode of the 4th metal-oxide-semiconductor M4, the grid of the first metal-oxide-semiconductor M1 connects the grid of the second metal-oxide-semiconductor M2, and the source electrode of the first metal-oxide-semiconductor M1 is connected in series the drain electrode that meets the second metal-oxide-semiconductor M2 after second capacitor C 2.

As shown in Figure 4, the tracking filter of bandwidth adjustable frequency, comprise first inductance L 1 and first capacitor C 1, it is characterized in that also comprising first to the 3rd metal-oxide-semiconductor M1～M3, first resistance R 1, the 3rd resistance R 3 and second capacitor C 2, wherein an end of first inductance L 1 connects an end of first capacitor C 1 respectively, one end of the 3rd resistance R 3, the drain electrode of the drain electrode of the first metal-oxide-semiconductor M1 and the 3rd metal-oxide-semiconductor M3, the other end of first inductance L 1 connects the other end of first capacitor C 1 respectively, the other end of the 3rd resistance R 3, one end of the source electrode of the second metal-oxide-semiconductor M2 and a resistance R 1, the grid of the first metal-oxide-semiconductor M1 connects the grid of the second metal-oxide-semiconductor M2, and the source electrode of the first metal-oxide-semiconductor M1 is connected in series the drain electrode that meets the second metal-oxide-semiconductor M2 after second capacitor C 2.

The described first metal-oxide-semiconductor M1 is the NMOS pipe.

The described second metal-oxide-semiconductor M2 is the NMOS pipe.

Described the 3rd metal-oxide-semiconductor M3 is the NMOS pipe.

Described the 4th metal-oxide-semiconductor M4 is the NMOS pipe.

1) when changing electric capacity, changes resistance, thereby keep the bandwidth approximately constant

$\mathrm{BW}=\frac{1}{2\mathrm{\π}(R-\mathrm{dig}*R_{\mathrm{step}})(C_{\min }+\mathrm{dig}*C_{\mathrm{step}})}\≈\frac{1}{2\mathrm{\πRC}}$

2) during practical application, can adopt the method for power transformation resistance step-length further to reduce the variation of bandwidth.

3) in order to reduce the resistance influence of mos switch, adopt the mode of big resistance parallel connection more feasible.NMOS can use PMOS instead, and difference is that control voltage will become.NMOS obtains switch closure with high level, and pmos obtains switch closure with low level.

Claims (8)

1. the tracking filter of a bandwidth adjustable frequency, comprise first resistance (R1), first inductance (L1) and first electric capacity (C1), it is characterized in that also comprising first, second metal-oxide-semiconductor (the M1, M2) and second electric capacity (C2), wherein an end of first resistance (R1) connects an end of first inductance (L1) respectively, the drain electrode of one end of first electric capacity (C1) and first metal-oxide-semiconductor (M1), the other end of first resistance (R1) connects the other end of first inductance (L1) respectively, the source electrode of the other end of first electric capacity (C1) and second metal-oxide-semiconductor (M2), the grid of first metal-oxide-semiconductor (M1) connects the grid of second metal-oxide-semiconductor (M2), and the source electrode of first metal-oxide-semiconductor (M1) is connected in series the drain electrode that meets second metal-oxide-semiconductor (M2) behind second electric capacity (C2).

2. the tracking filter of a bandwidth adjustable frequency, comprise first inductance (L1) and first electric capacity (C1), it is characterized in that also comprising first to the 3rd metal-oxide-semiconductor (M1～M3), first resistance (R1), the 3rd resistance (R3) and second electric capacity (C2), wherein an end of first inductance (L1) connects an end of first electric capacity (C1) respectively, one end of the 3rd resistance (R3), the drain electrode of the drain electrode of first metal-oxide-semiconductor (M1) and the 3rd metal-oxide-semiconductor (M3), the other end of first inductance (L1) connects the other end of first electric capacity (C1) respectively, the other end of the 3rd resistance (R3), one end of the source electrode of second metal-oxide-semiconductor (M2) and a resistance (R1), the grid of first metal-oxide-semiconductor (M1) connects the grid of second metal-oxide-semiconductor (M2), and the source electrode of first metal-oxide-semiconductor (M1) is connected in series the drain electrode that meets second metal-oxide-semiconductor (M2) behind second electric capacity (C2).

3. the tracking filter of bandwidth adjustable frequency according to claim 1 and 2 is characterized in that described first metal-oxide-semiconductor (M1) is the NMOS pipe.

4. the tracking filter of bandwidth adjustable frequency according to claim 1 and 2 is characterized in that described second metal-oxide-semiconductor (M2) is the NMOS pipe.

5. the tracking filter of bandwidth adjustable frequency according to claim 3 is characterized in that described the 3rd metal-oxide-semiconductor (M3) is the NMOS pipe.

6. the tracking filter of bandwidth adjustable frequency according to claim 1 and 2 is characterized in that described first metal-oxide-semiconductor (M1) is the PMOS pipe.

7. the tracking filter of bandwidth adjustable frequency according to claim 1 and 2 is characterized in that described second metal-oxide-semiconductor (M2) is the PMOS pipe.

8. the tracking filter of bandwidth adjustable frequency according to claim 3 is characterized in that described the 3rd metal-oxide-semiconductor (M3) PMOS pipe.

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