WO2000011783A1 - Tuned band-pass circuit - Google Patents

Tuned band-pass circuit Download PDF

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Publication number
WO2000011783A1
WO2000011783A1 PCT/EP1999/006164 EP9906164W WO0011783A1 WO 2000011783 A1 WO2000011783 A1 WO 2000011783A1 EP 9906164 W EP9906164 W EP 9906164W WO 0011783 A1 WO0011783 A1 WO 0011783A1
Authority
WO
WIPO (PCT)
Prior art keywords
terminal
image
coupled
band
pass circuit
Prior art date
Application number
PCT/EP1999/006164
Other languages
French (fr)
Inventor
Yeow T. Toh
Sheau C. Cheng
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2000011783A1 publication Critical patent/WO2000011783A1/en

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
    • H03J3/00—Continuous tuning
    • H03J3/24—Continuous tuning of more than one resonant circuit simultaneously, the circuits being tuned to substantially the same frequency, e.g. for single-knob tuning
    • H03J3/26—Continuous tuning of more than one resonant circuit simultaneously, the circuits being tuned to substantially the same frequency, e.g. for single-knob tuning the circuits being coupled so as to form a bandpass filter
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
    • H03J3/00—Continuous tuning
    • H03J3/02—Details
    • H03J3/16—Tuning without displacement of reactive element, e.g. by varying permeability
    • H03J3/18—Tuning without displacement of reactive element, e.g. by varying permeability by discharge tube or semiconductor device simulating variable reactance
    • H03J3/185—Tuning without displacement of reactive element, e.g. by varying permeability by discharge tube or semiconductor device simulating variable reactance with varactors, i.e. voltage variable reactive diodes
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
    • H03J5/00—Discontinuous tuning; Selecting predetermined frequencies; Selecting frequency bands with or without continuous tuning in one or more of the bands, e.g. push-button tuning, turret tuner
    • H03J5/24—Discontinuous tuning; Selecting predetermined frequencies; Selecting frequency bands with or without continuous tuning in one or more of the bands, e.g. push-button tuning, turret tuner with a number of separate pretuned tuning circuits or separate tuning elements selectively brought into circuit, e.g. for waveband selection or for television channel selection
    • H03J5/246—Discontinuous tuning; Selecting predetermined frequencies; Selecting frequency bands with or without continuous tuning in one or more of the bands, e.g. push-button tuning, turret tuner with a number of separate pretuned tuning circuits or separate tuning elements selectively brought into circuit, e.g. for waveband selection or for television channel selection using electronic means

Definitions

  • the invention relates to a tuned band-pass circuit, and to a television apparatus (TV, VCR, PC, etc) comprising such a tuned band-pass circuit.
  • a UHF band-pass circuit comprises a double-tuned tank circuit to provide good selectivity at selected RF frequency.
  • Image reject provision is achieved by a commonly used printed capacitance Ci as given in Fig. 1.
  • the top to top capacitance Ct not only controls the bandwidth at the high end of the band, but also indirectly limits the range of the image trap.
  • the disadvantage of this design is that the image trap range is always shorter than the RF range.
  • input susceptibility at N+5 (occurs at RF + 40 MHz, in between RF and image frequencies) will be difficult to achieve if the image trap falls exactly at image frequency Fi.
  • an object of the invention to provide an improved tuned bandpass circuit.
  • the invention provides a tuned band-pass circuit and a television apparatus as defined in the independent claims.
  • Advantageous embodiments are defined in the dependent claims.
  • a tunable band-pass circuit comprising a double-tuned tank circuit having a first terminal coupled to an input terminal and a second terminal coupled to an output terminal, and an image trap capacitance coupled between the input terminal and said second terminal, an image feedback capacitance is coupled between the output terminal and the input terminal.
  • Fig. 1 shows a typical UHF double tuned band-pass circuit having an image trap
  • Fig. 2 shows the location of the image trap in the band-pass filter design of Fig.
  • Fig. 3 shows an embodiment of a band-pass circuit with two image traps in accordance with the present invention
  • Fig. 4 shows a pictorial representation of the improvement derived from the two image traps in accordance with the present invention.
  • Fig. 5 shows an embodiment of a television apparatus in accordance with the present invention.
  • Fig. 1 shows a typical UHF double tuned band-pass circuit having an image trap.
  • a terminal I of a MOSFET MF is connected to a supply terminal thru a resistor R and a drain coil Ld.
  • the MOSFET terminal I is also coupled to a terminal Tl of a first tuning unit Lla, L2a, C2a, C3a, VCa thru a capacitor Cl.
  • the first tuning unit comprises coils Lla and L2a, capacitors C2a and C3a, and a varicap diode VCa connected as shown.
  • the circuit also comprises a second tuning unit Lla, L2a, C2a, C3a, VCa comprising coils Lib and L2b, capacitors C2b and C3b, and a varicap diode VCb connected as shown.
  • the top to top capacitance Ct is connected between first terminals Tl, T2 of the coils L2a and L2b, respectively, while second terminals of the coils L2a and L2b are connected to ground thru a coil L3.
  • a printed image trap capacitance Ci is connected between the MOSFET terminal I and the first terminal T2 of the coil L2b.
  • a band-pass to mixer coupling coil Lo connects the band-pass circuit to a mixer MIX.
  • Fig. 2 shows the location of the image trap Fit in the band-pass filter design of Fig. 1.
  • the uninterrupted line shows a realistic RF curve, while the dotted line is only optimized for image reject.
  • the proposed measure is to introduce an additional image feedback capacitance
  • a capacitance Co is present between the output terminal O and the mixer MIX.
  • FIG. 4 The pictorial representation of this additional image trap C+ can be found in Fig. 4.
  • the uninterrupted line shows a normal RF curve with a single image trap Ci, while the dotted line shows an RF curve with two image traps Ci and C+.
  • the results show that with the added C+ image trap, it broadens the rejection bandwidth that favors both N+5 and image rejection. Practical results have shown that both image reject and N+5 rejection have good buffers of at least 15 and 6 dB respectively at the lowest channel.
  • Fig. 5 shows an embodiment of a television apparatus (VCR, TV, PC) in accordance with the present invention.
  • An antenna A provides RF television signals to a tuner TUN comprising a double tunable band-pass circuit as shown in Fig. 3.
  • a video signal processing circuit VSP processes base-band video signals supplied by the tuner TUN; an output of the video signal processing circuit is coupled to a display terminal DT.
  • a display D is coupled to the display terminal DT.
  • the video signal processing circuit VSP includes everything needed to write signals on a recording medium (tape, disk) and to read signals from the recording medium.
  • the display D is then formed by a television set.
  • a primary aspect of the invention can be summarized as follows.
  • a supplementary printed image reject capacitance in the UHF band-pass circuit can improve both image reject and N+5 rejection by a great deal.
  • This invention can advantageously be used in analog and digital TV tuners, UHF band-pass, both in discrete and MOIC mixer oscillator configurations.
  • An embodiment of the invention thus provides a band-pass circuit comprising an image trap characterized in that the band-pass circuit comprises a supplementary trap.

Landscapes

  • Input Circuits Of Receivers And Coupling Of Receivers And Audio Equipment (AREA)

Abstract

In a tunable band-pass circuit, comprising a double-tuned tank circuit having a first terminal (T1) coupled (C1) to an input terminal (I) and a second terminal (T2) coupled (Lo) to an output terminal (O), and an image trap capacitance (Ci) coupled between the input terminal (I) and said second terminal (T2), a feedback capacitance (C+), an image feedback capacitance (C+) is coupled between the output terminal (O) and the input terminal (I) to improve image rejection.

Description

Tuned band-pass circuit.
The invention relates to a tuned band-pass circuit, and to a television apparatus (TV, VCR, PC, etc) comprising such a tuned band-pass circuit.
Typically, a UHF band-pass circuit comprises a double-tuned tank circuit to provide good selectivity at selected RF frequency. Image reject provision is achieved by a commonly used printed capacitance Ci as given in Fig. 1. The top to top capacitance Ct not only controls the bandwidth at the high end of the band, but also indirectly limits the range of the image trap. Thus, the disadvantage of this design is that the image trap range is always shorter than the RF range. Moreover, in a European UHF band design, input susceptibility at N+5 (occurs at RF + 40 MHz, in between RF and image frequencies) will be difficult to achieve if the image trap falls exactly at image frequency Fi.
One way to satisfy both image trap and input susceptibility is to place this trap between image frequency Fi and N+5 locations. Results will only be comfortable at higher end of the band where Q is the highest. Unfortunately, when the tuner is swept to the lower end of the band (where Q is lowest), performance is only marginal to both these parameters. It is difficult to maintain the true image trap Fit to fall optimally between these 2 locations at every part of the band. Even if it is possible, performance is also marginal at the low end where Q is smallest.
Let's say, if image reject trap ideally occurs at 2*IF = 77.8 MHz, then its image reject performance would definitely be typically 70 dB. However, input susceptivity at N+5 would then never satisfy its criteria. The best location of this image trap has to be optimized in between N+5 and image frequency Fi as in Fig. 2. In conclusion, the traditional optimized image trap (Ci) can only trade-off between image reject and N+5 susceptibility (refer to Fig. 2).
It is, inter alia, an object of the invention to provide an improved tuned bandpass circuit. To this end, the invention provides a tuned band-pass circuit and a television apparatus as defined in the independent claims. Advantageous embodiments are defined in the dependent claims. In a tunable band-pass circuit according to a primary aspect of the invention, comprising a double-tuned tank circuit having a first terminal coupled to an input terminal and a second terminal coupled to an output terminal, and an image trap capacitance coupled between the input terminal and said second terminal, an image feedback capacitance is coupled between the output terminal and the input terminal.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
In the drawings: Fig. 1 shows a typical UHF double tuned band-pass circuit having an image trap;
Fig. 2 shows the location of the image trap in the band-pass filter design of Fig.
1;
Fig. 3 shows an embodiment of a band-pass circuit with two image traps in accordance with the present invention;
Fig. 4 shows a pictorial representation of the improvement derived from the two image traps in accordance with the present invention; and
Fig. 5 shows an embodiment of a television apparatus in accordance with the present invention.
Fig. 1 shows a typical UHF double tuned band-pass circuit having an image trap. A terminal I of a MOSFET MF is connected to a supply terminal thru a resistor R and a drain coil Ld. The MOSFET terminal I is also coupled to a terminal Tl of a first tuning unit Lla, L2a, C2a, C3a, VCa thru a capacitor Cl. The first tuning unit comprises coils Lla and L2a, capacitors C2a and C3a, and a varicap diode VCa connected as shown. The circuit also comprises a second tuning unit Lla, L2a, C2a, C3a, VCa comprising coils Lib and L2b, capacitors C2b and C3b, and a varicap diode VCb connected as shown. The top to top capacitance Ct is connected between first terminals Tl, T2 of the coils L2a and L2b, respectively, while second terminals of the coils L2a and L2b are connected to ground thru a coil L3. A printed image trap capacitance Ci is connected between the MOSFET terminal I and the first terminal T2 of the coil L2b. A band-pass to mixer coupling coil Lo connects the band-pass circuit to a mixer MIX. Fig. 2 shows the location of the image trap Fit in the band-pass filter design of Fig. 1. The uninterrupted line shows a realistic RF curve, while the dotted line is only optimized for image reject.
The proposed measure is to introduce an additional image feedback capacitance
C+ (refer to Fig. 3). It is recommended to print this capacitance (typically 0.001 pF range by simulations) from the Mosfet drain to mixer input. In the embodiment, a capacitance Co is present between the output terminal O and the mixer MIX.
The pictorial representation of this additional image trap C+ can be found in Fig. 4. The uninterrupted line shows a normal RF curve with a single image trap Ci, while the dotted line shows an RF curve with two image traps Ci and C+. The results show that with the added C+ image trap, it broadens the rejection bandwidth that favors both N+5 and image rejection. Practical results have shown that both image reject and N+5 rejection have good buffers of at least 15 and 6 dB respectively at the lowest channel.
Fig. 5 shows an embodiment of a television apparatus (VCR, TV, PC) in accordance with the present invention. An antenna A provides RF television signals to a tuner TUN comprising a double tunable band-pass circuit as shown in Fig. 3. A video signal processing circuit VSP processes base-band video signals supplied by the tuner TUN; an output of the video signal processing circuit is coupled to a display terminal DT. A display D is coupled to the display terminal DT.
If the television apparatus of Fig. 5 is a VCR or another type of recorder, the video signal processing circuit VSP includes everything needed to write signals on a recording medium (tape, disk) and to read signals from the recording medium. The display D is then formed by a television set.
A primary aspect of the invention can be summarized as follows. A supplementary printed image reject capacitance in the UHF band-pass circuit can improve both image reject and N+5 rejection by a great deal. This invention can advantageously be used in analog and digital TV tuners, UHF band-pass, both in discrete and MOIC mixer oscillator configurations. An embodiment of the invention thus provides a band-pass circuit comprising an image trap characterized in that the band-pass circuit comprises a supplementary trap. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of other elements or steps than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

CLAIMS:
1. A tunable band-pass circuit, comprising: a double-tuned tank circuit having a first terminal (Tl) coupled (Cl) to an input terminal (I) and a second terminal (T2) coupled (Lo) to an output terminal (O); an image trap capacitance (Ci) coupled between said input terminal (I) and said second terminal (T2); and characterized by: an image feedback capacitance (C+) coupled between said output terminal (O) and said input terminal (I).
2. A television apparatus, comprising: a tuner (TUN) comprising a tunable band-pass circuit as claimed in claim 1; and video signal processing circuitry (VSP) between an output of said tuner and a display terminal (DT).
PCT/EP1999/006164 1998-08-25 1999-08-23 Tuned band-pass circuit WO2000011783A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
SG9800066 1998-08-25
SGPCT/SG98/00066 1998-08-25
EP99200996 1999-03-30
EP99200996.9 1999-03-30

Publications (1)

Publication Number Publication Date
WO2000011783A1 true WO2000011783A1 (en) 2000-03-02

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP1999/006164 WO2000011783A1 (en) 1998-08-25 1999-08-23 Tuned band-pass circuit

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WO (1) WO2000011783A1 (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002013383A1 (en) * 2000-08-10 2002-02-14 Infineon Technologies Ag High frequency input stage
EP2077618A1 (en) * 2007-12-28 2009-07-08 Alps Electric Co., Ltd. Double-tuning circuit of television tuner
EP2120337A1 (en) * 2008-05-12 2009-11-18 Alps Electric Co., Ltd. Voltage controlled oscillator including inter-terminal connection and trap circuit
EP2139112A1 (en) * 2008-06-25 2009-12-30 Alps Electric Co., Ltd. Double-tuned circuit

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06252706A (en) * 1993-02-26 1994-09-09 Alps Electric Co Ltd Input tuning circuit for tv tuner
DE19639238A1 (en) * 1995-09-25 1997-03-27 Alps Electric Co Ltd Input tuning circuit for television

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06252706A (en) * 1993-02-26 1994-09-09 Alps Electric Co Ltd Input tuning circuit for tv tuner
DE19639238A1 (en) * 1995-09-25 1997-03-27 Alps Electric Co Ltd Input tuning circuit for television

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 018, no. 646 (E - 1641) 8 December 1994 (1994-12-08) *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002013383A1 (en) * 2000-08-10 2002-02-14 Infineon Technologies Ag High frequency input stage
US6734761B2 (en) 2000-08-10 2004-05-11 Infineon Technologies Ag Radio-frequency input stage
EP2077618A1 (en) * 2007-12-28 2009-07-08 Alps Electric Co., Ltd. Double-tuning circuit of television tuner
US7852177B2 (en) 2007-12-28 2010-12-14 Alps Electric Co., Ltd. Double-tuning circuit of television tuner
EP2120337A1 (en) * 2008-05-12 2009-11-18 Alps Electric Co., Ltd. Voltage controlled oscillator including inter-terminal connection and trap circuit
EP2139112A1 (en) * 2008-06-25 2009-12-30 Alps Electric Co., Ltd. Double-tuned circuit

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