CN1187913A

CN1187913A - Interstage electric filter for tuner

Info

Publication number: CN1187913A
Application number: CN96194793A
Authority: CN
Inventors: F·阿什万德恩
Original assignee: RCA Licensing Corp
Current assignee: RCA Licensing Corp
Priority date: 1995-04-27
Filing date: 1996-04-26
Publication date: 1998-07-15

Abstract

In a tuner, a tunable bandpass filter which has a combined high side coupling portion having an increasing coefficient of coupling with increasing frequency and a low side coupling portion having a decreasing coefficient of coupling with increasing frequency. The two coefficients of coupling vary inversely with frequency with respect to each other as the bandpass filter is tuned through the frequency band.

Description

Tunable inter-stage filter

Invention field

The present invention relates to be used for the tunable inter-stage filter of tuner.

Background of invention

Current, the tuner work that is used for the various digital transmission system received digital signals that processing and utilizing proposes now gets not very good.Because it is much serious to the influence of the influence comparison analog signal of digital signal that digital signal has occupied whole frequency spectrums of channel and time-delay and frequency response error, so the RF of receiver and IF characteristic all need to improve.And, because the transmitting power of digital signal is less than the transmitting power of analog signal, so receiving required digital signal satisfactorily may be difficult more, especially true when existing strong side channel signal.

Therefore, need to improve the RF filtering that enters frequency mixer tuner before, particularly reduce the influence of strong side channel.

Brief summary of the invention

In brief, tunable band pass filter is used for processing RF signals before frequency mixer.This band pass filter has the high-end coupling unit and the low side coupling portion of combination, and the coupling coefficient of high-end coupling unit increases with the raising of frequency, and the coupling coefficient of low side coupling portion then reduces with the raising of frequency.When tuning this band pass filter in whole frequency, these two kinds of coupling coefficients reciprocally change relatively with frequency.

Brief description of drawings

Fig. 1 illustrates the block diagram that comprises according to the tuner circuit of the inter-stage band pass filter of prior art;

Fig. 2 a～2d is the schematic diagram of various bandwidth-limited circuits, and Fig. 2 a and 2b illustrate the circuit according to prior art, and Fig. 2 c and 2d illustrate the filter circuit of the various aspects according to the present invention;

Fig. 3 illustrates the tuner circuit of Fig. 1 of the filter circuit schematic diagram that has shown in Fig. 2 d, and the filter of Fig. 2 d of various aspects is as the inter-stage band pass filter according to the present invention.

Detailed description of preferred embodiment

Fig. 1 illustrates a kind of RF tuner according to prior art, and it comprises: single tuning input tape bandpass filter 10; 1RF amplifier 12, it is generally the bigrid MOSFET amplifier of AGC controllable gain; Double tunning inter-stage filter 14; And the 2nd RF amplifier 16, the output signal of amplifier 16 is coupled to and is used for the frequency mixer (not shown) of the RF signal frequency that conversion process crosses.In common circuit, band pass filter 14 be tuned to upper frequency through regular meeting its passband response is broadened, and, can make the input of filter 14 and output and between the corresponding output end of

amplifier

12 and 16 and input impedance mismatching.

Fig. 2 a～2d illustrates multiple double tunning band pass filter, wherein, the element with identical function is marked with identical symbol.Fig. 2 a illustrates the double tunning band pass filter that has high-end coupling, promptly, by high end capacitor Cx the input of being made up of two adjustable condenser C1 (because the capacitance of these two capacitors is basic identical, so they are symbolization C1 all) and inductance L is coupled together with the output tuning circuit.Fig. 2 b illustrates the double tunning band pass filter that has the low side coupling, that is, by low side coupling capacitor Cy input of being made up of adjustable condenser C1 and inductance L and output tuning circuit are coupled together.

To the high-end strap bandpass filter of Fig. 2 a, the capacitance that the coupling coefficient between input and output is approximately equal to capacitor Cx removed by the long-pending square root of two adjustable condenser C1 capacitances and must the merchant.Like this, the coupling coefficient K of band pass filter shown in Fig. 2 a and the square root of C1 are inversely proportional to.By the value of capacitor C1 is adjusted to less capacitance, just make filter tuner shown in Fig. 2 a to upper frequency.Like this, coupling coefficient K will be along with this filter tuner is increased to upper frequency.For the low side strap bandpass filter shown in Fig. 2 b, the coupling coefficient between input and output is approximately equal to the square root of product of two capacitor C1 capacitances again divided by the merchant of the capacitance gained of capacitor Cy.Like this, the coupling coefficient K of band pass filter shown in Fig. 2 b is directly proportional with the square root of C1 (for formula high-end and the low side coupling, see " ITT radio engineer reference data (ITT Reference Data for RadioEngineer) " the 4th edition, version in 1956, the 238th page).By the value of capacitor C1 is adjusted to less capacitance, just make filter tuner shown in Fig. 2 b to upper frequency.Like this, coupling coefficient will be along with this filter tuner is reduced to upper frequency.The inventor has recognized that, when the value that reduces capacitor C1 so that corresponding band pass filter from lower frequency be tuned to during upper frequency, the coupling coefficient of the low side coupling filter of the coupling coefficient of the high-end coupling filter of Fig. 2 a and Fig. 2 b changes with reciprocal relation.Based on this understanding, the inventor has invented the inter-stage filter of new excellence.They are shown in Fig. 2 c and 2d.

Fig. 2 c illustrates a kind of double tunning band pass filter, and it turns back to ground, also capacitor Cx is coupled between the high end capacitor C1 by capacitor C1 being passed through capacitor Cy, thereby the high-end coupling circuit of Fig. 2 a and 2b and low side coupling circuit are combined.According to various aspects of the present invention high-end coupling and low side coupled combination are got up, when the filter of this combinational circuit from lower frequency be tuned to during upper frequency, the variation of coupling coefficient will appear on a certain position between two of filter shown in Fig. 2 a and the 2b are extreme.For example, because the coupling of capacitor Cx (high-end) and Cy (low side) has opposite relation to tuned frequency, so, by suitably selecting the value of capacitor Cx and Cy, when by regulating these two capacitor C1 in this frequency range during tuning inter-stage filter, can in whole tuning range, obtain substantially invariable coupling coefficient and substantially invariable input, outlet terminal impedance, thereby reduce to have the impedance mismatching of the inter-stage filter of

amplifier

12 and 16.

By filter shown in Fig. 2 c is carried out the conversion of Y-Δ, can obtain the another kind of circuit shown in Fig. 2 d.Above the related coupling coefficient of double tunning inter-stage filter of relevant Fig. 2 c to frequency and tuning discussion, also be applicable to shown in Fig. 2 d in the double tunning band pass filter.

Fig. 3 shows a kind of tuner circuit that is used for uhf band, and its utilize to insert a filter according to Fig. 2 d to replace the inter-stage filter 14 among Fig. 1.Each capacitor Cx, Cy, and C1 can comprise parasitism and the stray electrical capacity relevant with the described electric capacity shown in the circuit.Inductance L is provided by band like thread elements, and these elements are coupled to ground, and they provide DC loop to tunable varactor

diode C1.Amplifier

12 and 16 has the input and the output impedance in 50 Europe, and 25dB and 8dB are provided respectively gain.By at terminal V _tOn suitable tuning voltage V _tBe added to through resistance R on the anode of varactor capacitor C1 of coupling to realize the tuning of filter 14.As very common in modern tuner, be used for inter-stage filter and other tunable devices (not shown) be tuned to tuning voltage V on the required frequency _t, can produce by DAC (not showing) according to the tuning voltage value of reading by the microprocessor (not shown) from EPROM.As also having known in this technology, tuning voltage also can be produced by phase-locked loop.

In one exemplary embodiment shown in Figure 3,

amplifier

12 and 16 is respectively MAR-8 and the MAR-4 that New York, United States Brooklyn city Mini-Circuit (mini circuit) company makes.Tuning capacitor C1 is the two variable capacitance diode BBY62 of monolithic that Dutch Philips (Philips) company makes.

Claims

1. a band pass filter has signal input part and signal output part, and is tunable in the whole frequency from the lower frequency to the upper frequency, comprising:

High-end coupling unit with the coupling coefficient that increases with increase frequency from described lower frequency to described upper frequency, and

Low side coupling portion with the coupling coefficient that reduces with increase frequency from described lower frequency to described upper frequency;

When tuning described band pass filter in described frequency range, the described coupling coefficient of described high-end coupling unit and the described coupling coefficient of described low side coupling portion are on the contrary with frequency and change.

2. according to the filter described in the claim 1, it is characterized in that, the inverse variation of the described coupling coefficient of wherein said high-end coupling unit and the described coupling coefficient of described low side coupling portion is complementary, so that carry out in described frequency range when tuning, the coupling coefficient of described band pass filter between described input and described output keeps constant basically.

3. a band pass filter has signal input part and signal output part, and is tunable comprising in a frequency range:

Be coupled to the 1st inductance between described input and the reference point,

Be coupled to the 1st capacitor between described input and the node,

Be coupled to the 2nd capacitor between described node and the described reference point,

Be coupled to the 3rd capacitor between described output and the described node,

Be coupled to the 2nd inductance between described output and the described reference point, and

Be coupled to the 4th capacitor between described input and the described output;

The the described the 1st and the 3rd capacitor is adjustable;

Select the value of described the 2nd capacitor and described the 4th capacitor so that when by regulating the described the 1st and the 3rd capacitor in described frequency range during tuning described band pass filter, described band pass filter will have substantially invariable coupling coefficient.

4. a band pass filter has signal input part and signal output part, and is tunable in a frequency range, comprising:

Be coupled to the 1st capacitor between described input and the 1st node,

Be coupled to the 2nd capacitor between described the 1st node and the described reference point,

Be coupled to the 3rd capacitor between described output and the 2nd node,

Be coupled to the 4th capacitor between described the 2nd node and the described reference point,

Be coupled to the 2nd inductance between described output and the described reference point,

Be coupled to the 5th capacitor between described input and the described output, and

Be coupled to the 6th capacitor between described the 1st node and described the 2nd node;

The the described the 1st and the 3rd capacitor is adjustable;

Select the value of described the 4th capacitor and described the 5th capacitor so that when by regulating the described the 1st and the 3rd capacitor in described frequency range during tuning described band pass filter, described band pass filter will have substantially invariable coupling coefficient.

5. a band pass filter has signal input part and signal output part, and is tunable in a frequency range, comprising:

Be coupled to the 1st inductance between described input and the reference point;

Be coupled to the 1st capacitor between described input and the node;

Be coupled to the 2nd capacitor between described node and the described reference point;

Be coupled to the 3rd capacitor between described output and the described node;

Be coupled to the 2nd inductance between described output and the described reference point; And

Be coupled to the 4th capacitor between described input and the described output.

6. according to the band pass filter described in the claim 5, it is characterized in that wherein, the described the 1st and the 3rd capacitor is adjustable.

7. according to the band pass filter described in the claim 6, it is characterized in that, to select the value of described the 2nd capacitor and described the 4th capacitor like this, so that when by regulating the described the 1st and described the 3rd capacitor and in described frequency range during tuning described band pass filter, described band pass filter will have substantially invariable coupling coefficient.

8. a band pass filter has signal input part and signal output part, and is tunable in a frequency range, comprising:

Be coupled to the 1st capacitor between described input and the 1st node;

Be coupled to the 2nd capacitor between described the 1st node and the described reference point;

Be coupled to the 3rd capacitor between described output and the 2nd node;

Be coupled to the 4th capacitor between described the 2nd node and the described reference point;

Be coupled to the 2nd inductance between described output and the described reference point;

Be coupled to the 5th capacitor between described input and the described output; And

Be coupled to the 6th capacitor between described the 1st node and described the 2nd node.

9. the band pass filter described in according to Claim 8 is characterized in that the wherein said the 1st and the 3rd capacitor is adjustable.

10. according to the band pass filter described in the claim 9, it is characterized in that, to select the value of described the 4th capacitor and described the 5th capacitor like this, so that when by regulating the described the 1st and described the 3rd capacitor and in described frequency range during tuning described band pass filter, described band pass filter will have substantially invariable coupling coefficient.