CN102131063A - Active loop low-pass filter matched with digital TV tuning chip - Google Patents
Active loop low-pass filter matched with digital TV tuning chip Download PDFInfo
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- CN102131063A CN102131063A CN2011100085650A CN201110008565A CN102131063A CN 102131063 A CN102131063 A CN 102131063A CN 2011100085650 A CN2011100085650 A CN 2011100085650A CN 201110008565 A CN201110008565 A CN 201110008565A CN 102131063 A CN102131063 A CN 102131063A
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Abstract
The invention particularly relates to an active loop low-pass filter matched with a digital TV tuning chip, which comprises a resistor R1 and a capacitor C1 connected in parallel, and a parallel circuit and a capacitor C2 are connected in series. The filter also comprises a variable capacitance diode U1, wherein the variable capacitance diode U1 is connected with the capacitor C1 in series and then is connected with the resistor R1 in parallel. One end of the parallel circuit is connected with a VTU (Versatile Timer Unit) interface of the digital TV tuning chip, and the other end of the capacitor C2 is connected with a CP (Charge Pump) interface of the digital TV tuning chip. Through the active loop low-pass filter matched with the digital TV tuning chip, the loop noise is reduced, and the output quality of signals is improved.
Description
Technical field
The present invention relates to satellite digital television receiving system, be specifically related to a kind of and active loop low pass filter Digital Television tuning chip cooperating.
Background technology
In satellite digital television receiving system, in recent years along with the development of Digital Television, present digital tuning chip more and more can not satisfy the requirement of high-frequency input signal, the operating current maximum of the charge pump of present digital tuning chip is about 900uA, when the frequency ratio of input signal is higher, because of can not matching, the operating current of charge pump tends to produce loop noise, influenced the quality of output signal, therefore need to improve the operating current of charge pump, improve the operating current of charge pump, can reduce the noise of local oscillated signal near-end greatly, but also can worsen the noise of local oscillated signal far-end simultaneously.
Summary of the invention
The purpose of this invention is to provide a kind of with have the active loop low pass filter of the digital tuning chip cooperating of large-current electric lotus pump, reduce signal noise, improve the output quality of signal.
For achieving the above object, the present invention has adopted following technical scheme, this device comprises resistance R 1 and the capacitor C 1 that is connected in parallel, this parallel circuits and capacitor C 2 are connected in series, it is characterized in that: this filter also comprises variable capacitance diode U1, and variable capacitance diode U1 is with in parallel with resistance R 1 again after described capacitor C 1 is connected, the VTU interface of a termination digital tuning chip of this parallel circuits, other end serial connection capacitor C 2, the CP interface of another termination digital tuning chip of described capacitor C 2.
As shown from the above technical solution, when the frequency of input signal is higher, can select big operating current, can reduce the noise of local oscillations (referring to VHF-H oscillator 4 and UHF oscillator 5) signal near-end so greatly, but also can worsen the noise of local oscillated signal far-end simultaneously, so with the active loop low pass filter of digital tuning chip cooperating in added variable capacitance diode U1, when cut-ff voltage is big more, the electric capacity of U1 is more little, so when the operating current of charge pump increases, tuning voltage (voltage at VTU place) increases, the electric capacity of U1 diminishes so, and the equivalent capacity of U1 and C1 diminishes, and then the bandwidth of active loop low pass filter diminishes, be that cut-off frequency diminishes, suppressed the noise of local oscillations far-end effectively.
Description of drawings
Fig. 1 is the circuit theory diagrams of digital tuning chip;
Fig. 2 is the circuit theory diagrams of active loop low pass filter.
Embodiment
As shown in Figure 1, the Digital Television tuning chip comprises clock generator 1, programmable frequency divider 2, VHF-H frequency mixer 3, VHF-H oscillator 4, UHF oscillator 5, UHF frequency mixer 6, intermediate frequency sound table driving amplifier 7, radio frequency wave detector 8, pre-divider 9, phase discriminator 10, charge pump 11, general purpose I/O circuit 12, intermediate frequency automatic gain control amplifier 13, I2C controller 14, charge pump 11, the operating current of charge pump 11 are seven grades: 70uA, 140uA, 350uA, 600uA, 900uA, 1.5mA, maximum operating currenbt reaches 1.5mA.
The operating current of charge pump is to realize that by the BandSwitch Byte position that is provided with in I2C controller 14 registers configuration definition of Band Switch Byte is:
After externally main frame is selected Band Switch Byte, each is configured, concrete current arrangements table is as shown in the table.
When tuning voltage during greater than 20V, the operating current of charge pump 11 is set to 1.5mA.
The operating current of charge pump 11 is that external host is selected by I2C controller 14 according to different frequency ranges, and when tuning voltage during greater than 20V, the operating current of charge pump 11 is set to 1.5mA through test repeatedly, and the currents match degree is best, and loop noise is minimum.The lower limit of the high band of the frequency values correspondence of this moment, external host judge when the frequency values of input signal is worth greater than this, and the operating current that charge pump is set to I2C controller 14 that sends instructions is 1.5mA.
When the frequency of input signal is positioned at high band, the operating current of charge pump is set to maximum operating currenbt 1.5mA, can reduce the noise of local oscillated signal near-end greatly, but also can worsen the noise of local oscillated signal far-end simultaneously, so when using than large charge pump electric current, need reduce the bandwidth with the active loop low pass filter of digital tuning chip cooperating, therefore, the active loop low pass filter also be improved.
As shown in Figure 2, the active loop low pass filter comprises resistance R 1 and the capacitor C 1 that is connected in parallel, this parallel circuits and capacitor C 2 are connected in series, this filter also comprises variable capacitance diode U1, described variable capacitance diode U1 is with in parallel with resistance R 1 again after described capacitor C 1 is connected, the VTU interface of the described digital tuning chip of one termination claim 1 of this parallel circuits, other end serial connection capacitor C 2, the CP interface of another termination digital tuning chip of described capacitor C 2.
VTU and CP are connected to the VTU pin and the CP pin of chip respectively, constitute active loop low pass filter with the amplifier of die terminals.Mainly by the equivalent capacity decision of U1 and C1, the equivalent capacity of U1 and C1 is U1*C1/ (U1+C1) to the bandwidth of active loop low pass filter.Tuning voltage has determined the frequency of local oscillations and the capacitance of U1 simultaneously, so when local oscillating frequency changed, the bandwidth of loop filter also changed at the same time.Variable capacitance diode U1, when cut-ff voltage is big more, the electric capacity of U1 is more little, so when the operating current of charge pump increased, tuning voltage increased, the electric capacity of U1 diminishes so, the equivalent capacity U1*C1/ of U1 and C1 (U1+C1) diminishes, then the bandwidth of active loop low pass filter diminishes, and promptly cut-off frequency diminishes, thereby has suppressed the noise of local oscillations far-end effectively.
Claims (1)
1. active loop low pass filter with Digital Television tuning chip cooperating, comprise the resistance R 1 and the capacitor C 1 that are connected in parallel, this parallel circuits and capacitor C 2 are connected in series, it is characterized in that: this filter also comprises variable capacitance diode U1, described variable capacitance diode U1 is with in parallel with resistance R 1 again after described capacitor C 1 is connected, the VTU interface of one termination digital tuning chip of this parallel circuits, other end serial connection capacitor C 2, the CP interface of another termination digital tuning chip of described capacitor C 2.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2011100085650A CN102131063A (en) | 2011-01-16 | 2011-01-16 | Active loop low-pass filter matched with digital TV tuning chip |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2011100085650A CN102131063A (en) | 2011-01-16 | 2011-01-16 | Active loop low-pass filter matched with digital TV tuning chip |
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| Publication Number | Publication Date |
|---|---|
| CN102131063A true CN102131063A (en) | 2011-07-20 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN2011100085650A Pending CN102131063A (en) | 2011-01-16 | 2011-01-16 | Active loop low-pass filter matched with digital TV tuning chip |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103001630A (en) * | 2011-09-08 | 2013-03-27 | 阿尔卑斯电气株式会社 | Phase synchronication circuit and television signal reception circuit |
Citations (6)
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| US5170130A (en) * | 1990-09-19 | 1992-12-08 | Nec Corporation | Phase lock loop circuit with a subsidiary loop filter |
| US20070200637A1 (en) * | 2006-02-22 | 2007-08-30 | Fujitsu Limited | PLL circuit and semiconductor device |
| CN101179262A (en) * | 2006-11-09 | 2008-05-14 | 西门子公司 | Filter circuit device |
| CN101485093A (en) * | 2006-06-30 | 2009-07-15 | 高通股份有限公司 | Loop filter with noise cancellation |
| US20090237131A1 (en) * | 2008-03-21 | 2009-09-24 | Broadcom Corporation | Phase locked loop |
| CN101917176A (en) * | 2010-08-20 | 2010-12-15 | 复旦大学 | Cut-off frequency self-tuning method and circuit for filter |
-
2011
- 2011-01-16 CN CN2011100085650A patent/CN102131063A/en active Pending
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5170130A (en) * | 1990-09-19 | 1992-12-08 | Nec Corporation | Phase lock loop circuit with a subsidiary loop filter |
| US20070200637A1 (en) * | 2006-02-22 | 2007-08-30 | Fujitsu Limited | PLL circuit and semiconductor device |
| CN101485093A (en) * | 2006-06-30 | 2009-07-15 | 高通股份有限公司 | Loop filter with noise cancellation |
| CN101179262A (en) * | 2006-11-09 | 2008-05-14 | 西门子公司 | Filter circuit device |
| US20090237131A1 (en) * | 2008-03-21 | 2009-09-24 | Broadcom Corporation | Phase locked loop |
| CN101917176A (en) * | 2010-08-20 | 2010-12-15 | 复旦大学 | Cut-off frequency self-tuning method and circuit for filter |
Non-Patent Citations (1)
| Title |
|---|
| 刘奡: "宽带PLL环路滤波器的设计", 《中国优秀硕士学位论文全文数据库-信息科技辑》 * |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103001630A (en) * | 2011-09-08 | 2013-03-27 | 阿尔卑斯电气株式会社 | Phase synchronication circuit and television signal reception circuit |
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Application publication date: 20110720 |