EP1632027A1 - Selecteur de canaux a commande automatique de gain - Google Patents

Selecteur de canaux a commande automatique de gain

Info

Publication number
EP1632027A1
EP1632027A1 EP04734584A EP04734584A EP1632027A1 EP 1632027 A1 EP1632027 A1 EP 1632027A1 EP 04734584 A EP04734584 A EP 04734584A EP 04734584 A EP04734584 A EP 04734584A EP 1632027 A1 EP1632027 A1 EP 1632027A1
Authority
EP
European Patent Office
Prior art keywords
switched
agc
attenuator
channel
preamplifier
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP04734584A
Other languages
German (de)
English (en)
Inventor
Kam C. c/o Philips I.P. & StandardsGmbh Kwong
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
NXP BV
Original Assignee
Koninklijke Philips Electronics NV
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 NV filed Critical Koninklijke Philips Electronics NV
Publication of EP1632027A1 publication Critical patent/EP1632027A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers
    • H03G3/20—Automatic control
    • H03G3/30—Automatic control in amplifiers having semiconductor devices
    • H03G3/3052—Automatic control in amplifiers having semiconductor devices in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver
    • H03G3/3068—Circuits generating control signals for both R.F. and I.F. stages
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
    • H04N5/52—Automatic gain control
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G1/00—Details of arrangements for controlling amplification
    • H03G1/0005—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal
    • H03G1/0088—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal using discontinuously variable devices, e.g. switch-operated

Definitions

  • the invention relates to a channel selector comprising in cascade a gain- controlled RF preamplifier for amplifying received RF channel signals, a mixing stage for converting the amplified RF channel signals to IF channel signals, an IF filter connected to the output of the mixing stage for selecting a desired channel signal from said IF channel signals and means connected to the output of the IF filter for deriving from the selected IF channel signal an AGC voltage that reduces the gain of the RF preamplifier in a high level mode, when the level of said selected IF channel signal is above a predetermined level, and that keeps the gain of the RF preamplifier substantially constant in a low level mode, when the level of said selected IF channel signal is below said predetermined level.
  • Such channel selector is well known in the art and serves to derive from a plurality of received RF channel signals one desired IF channel signal with the best possible signal to noise (S/N) ratio and without substantial non-linear distortion.
  • the antenna input signal may have a S/N-ratio of 51 ,3 dB and the tuning arrangement itself may have a noise figure of 4 dB, so that the S/N-ratio at IF is 47,3 dB.
  • the automatic gain control is a so-called delayed AGC with a low level mode in which the input signal level and consequently also the IF output level is so low that a gain reduction of the RF preamplifier is not appropriate.
  • TOP take over point
  • the automatic gain control enters the high level mode wherein the gain of the RF preamplifier is reduced so as to maintain the IF output level substantially constant.
  • a channel selector has to be used for the reception of off-the-air signals as well as for the reception of signals from cable systems.
  • the input signal may be substantially stronger than 60 dB ⁇ V, for instance 66 dB ⁇ V.
  • the automatic gain control (AGC) of the RF preamplifier reduces the gain of this stage as soon as the level of the IF output signal is stronger than e.g.105 dB ⁇ V, the "take over point" (TOP).
  • a drawback however is that every dB gain reduction of the RF preamplifier increases the noise factor of the tuning arrangement by one dB, so that the S/N-ratio at stronger input signals remains at the S/N-ratio at the "take over point".
  • the tuning arrangement according to the present invention is therefore characterized by a switched attenuator between the output of the mixer and the input of the IF filter, said switched attenuator being controlled by the AGC voltage so that it is operative in at least part of said high level mode and non operative in at least part of said low level mode.
  • the end-result is that the IF output signal is at the original level but with improved signal to noise ratio, because the addition of noise by the preamplifier is reduced while the attenuator itself does not substantially add noise. For instance, at 66 dB ⁇ V input level and a 6 dB attenuator the AGC loop will react as if the input level would be 60 dB ⁇ V, with the result that the noise figure of the preamplifier is 6 dB less. It will be apparent that the extent of the added attenuation is limited by the capability of the mixer and of the IF-path in front of the attenuator to handle larger signals without distortion problems.
  • the channel selector according to the present invention may further be characterized by a switched amplifier connected in parallel with said switched attenuator, said switched amplifier being controlled by the AGC voltage so that it is operative in a part of said low level mode in which the switched attenuator is not operative.
  • the switched amplifier improves the dynamic range at the low signal levels.
  • the switched amplifier does not improve the signal to noise ratio because the AGC is not active in this range and thus the IF signal and the accompanying noise are equally amplified by the switched amplifier.
  • the switched amplifier does increase the lower IF signal levels and therewith the sensitivity of the channel selector, i.e. the smallest signal which gives a useful picture.
  • the amplifier should be switched off before the high end of the low level mode is reached, so as to prevent that the AGC becomes operative with the extra noise then added. For instance, when the input level of the "take over point" lies at 60 dB ⁇ V and the switched amplifier has a gain of 10 dB, the amplifier should be switched off at an input level at or lower than 50 dB ⁇ V. It is remarked that a continuous IF AGC in combination with RF AGC is known in the art, for instance from U.S. Patent
  • Such double AGC is useful in receivers with a digital demodulator to obtain a high and constant IF level over a large range of input levels.
  • the channel selector according to the invention is further characterized in that the switched attenuator and the switched amplifier are each switched by a comparator that compares the said AGC voltage with a predetermined DC voltage.
  • Figure 1 a block diagram of a channel selector according to the invention
  • Figure 2 a graph for explaining the operation of the channel selector of figure 1 and
  • Figure 3 a detailed schematic diagram of a switched attenuator and switched amplifier for use in the channel selector of figure 1.
  • the channel selector of figure 1 comprises a first tuned filter 2 whose input may be connected to an antenna 1 and whose output is connected to the input of an RF preamplifier 3.
  • the RF channel signals amplified by the preamplifier 3 are fed through a second tuned filter 4 to a mixer 5 where the RF signals are multiplied with an oscillation from a tuned local oscillator 6.
  • the mixer converts the RF signals to intermediate frequency (IF) signals that are subsequently amplified in an IF amplifier 7 and supplied to a surface acoustic wave filter 8 where the channel filtering takes place.
  • IF intermediate frequency
  • the tuned filters 1 and 4 do substantially not attribute to the channel filtering but serve primarily to suppress the image frequencies that would otherwise fold into the desired IF channel in the mixer 5.
  • the desired IF channel signal is applied to an IF unit 9 where further IF amplification and IF demodulation takes place.
  • the IF unit 9 generates an automatic gain control (AGC) voltage V agc for controlling the gain of the preamplifier 3.
  • AGC automatic gain control
  • the point where the AGC voltage starts reducing the gain of the preamplifier is the "take over point" (TOP).
  • TOP take over point
  • a delay device e.g. a single diode
  • the channel selector of figure 1 comprises a switched attenuator 10 and a switched amplifier 1 1 between the output A of the IF amplifier 7 and the input B of the SAW filter 8.
  • the attenuator 10 can be switched “on” and “off by means of a comparator Ci that compares the AGC-voltage V a c with a predetermined reference voltage V ⁇ and the amplifier 11 can be switched “on” and “off by means of a comparator C 2 that compares the AGC-voltage with a predetermined reference voltage V 2 .
  • the combination provides a reference gain that is not necessarily equal to 0 dB.
  • the switched amplifier is "on” its gain is increased by e.g. 10 dB and when the switched attenuator is "on” its gain is decreased by e.g. 6 dB.
  • the amplifier and the attenuator should not be “on” simultaneously.
  • the operation of the switched attenuator and the switched amplifier is illustrated in the diagram of figure 2 that shows the IF level V 0 at the output of the SAW filter 8 in dB ⁇ V as a function of the antenna input level V, also in dB ⁇ V.
  • the dashed line in figure 2 represents this function without the attenuator 10 and the amplifier 11.
  • the amplifier 11 is "on” and the sensitivity of the arrangement is increased by e.g. 10 dB.
  • the level increases switches off at an input level L 2 of e.g. 50 dB ⁇ V.
  • the level passes the "take over point" that is situated at an input level T of e.g. 63 dB ⁇ V.
  • the attenuator 10 is switched on so that from this level on the signal to noise ratio of the arrangement is increased.
  • FIG 3 shows a detailed implementation of the switched attenuator 10 and the switched amplifier 11 of figure 1.
  • the switched amplifier comprises a bipolar npn transistor Ti with an emitter impedance of resistors Ri, R 2 and bypass capacitor C ⁇ , an inductance Li in the collector lead and a feedback resistor R in series with a capacitor C 3 between the collector- and base-electrodes of the transistor.
  • IF input signals from IF-amplifier 7 of figure 1 are applied, through input terminal A and a capacitor C 2 to the base electrode of the transistor Ti and the amplified signals from the collector electrode are applied through a capacitor C 4 and via output terminal B to the input of the SAW filter 8 of figure 1.
  • the transistor Ti is switched on and off by means of a switching transistor T 2 that is controlled by the comparator C 2 .
  • the collector electrode of this switching transistor is connected through a collector resistor R 4 to the supply voltage and through a series resistor R5 to the base electrode of the amplifier transistor T,.
  • the switched attenuator comprises, between the IF input terminal A and the IF output terminal B the series arrangement of a capacitor C 5 , a resistor R ⁇ , a diode Di, a second diode D 2 , a resistor R 7 and a capacitor C O .
  • a resistor Rs couples the interconnected anodes of the diodes Di and D 2 to the positive supply voltage.
  • the collector electrode of a switching transistor T 3 is connected through a resistor R 9 to the interconnection of C 5 and R « and through a resistor Rio to the interconnection of C O and R 7 .
  • the comparator Ci controls the switching transistor T 3 .
  • the values of the passive components of the arrangement of figure 3 are as follows:
  • capacitors C 2 to C ⁇ have only a DC-separation function and that the resistors R 4 , R 9 and Rio have only a DC-supplying function.
  • the automatic gain control voltage V agc is high with the result that both the comparators Ci and C deliver low output voltages and that consequently the switching transistors T 2 and T 3 are cut off.
  • the diodes Di and D 2 are non-conducting so that the switched attenuator is off.
  • the amplifier transistor Ti is conducting and the IF signal from the input A is amplified by the transistor Ti to the output B.
  • the voltage V agc passes the predetermined voltage V 2 so that the output of the comparator C becomes high, the switching transistor T 2 becomes conducting and the transistor Ti is cut off.
  • the IF signals from the input terminal are not any more amplified, but pass unamplified through the capacitor C 2 , the feedback path C 3 , R 3 and the capacitor C to the output terminal B.
  • resistor R 3 determines the reference gain, i.e. the gain between the terminals A and B when both the amplifier and the attenuator are off.
  • the input signal passes the level Li of figure 2
  • the voltage Va g c passes the predetermined voltage Vi and the output of the comparator becomes high, with the result that the switch transistor T 3 and the attenuator diodes Di and D become conducting.
  • the attenuator is in the "on"-state.
  • the attenuator which is formed by the three resistors Re, R and Rg is configured so that its output impedance is maintained as close as possible to the output impedance of the switched amplifier in the "on"-state.

Landscapes

  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Control Of Amplification And Gain Control (AREA)
  • Circuits Of Receivers In General (AREA)

Abstract

L'invention concerne un sélecteur de canaux comportant un pré-amplificateur RF et un mélangeur pour convertir les signaux d'entrée RF en signaux de sortie de fréquence intermédiaire. Dans ledit sélecteur de canaux, une tension de commande automatique de gain (AGC) est dérivée des signaux de sortie IF en vue de réduire le gain du pré-amplificateur RF après un point de transfert de commande (temporisation AGC). Dans le trajet de sortie IF du mélangeur est disposé un atténuateur commuté sur marche et arrêt sous la commande de la tension de gain automatique . L'atténuateur est sur marche à des niveaux supérieurs au point de transfert de commande .
EP04734584A 2003-05-27 2004-05-24 Selecteur de canaux a commande automatique de gain Withdrawn EP1632027A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IB0303970 2003-05-27
PCT/IB2004/050758 WO2004107574A1 (fr) 2003-05-27 2004-05-24 Selecteur de canaux a commande automatique de gain

Publications (1)

Publication Number Publication Date
EP1632027A1 true EP1632027A1 (fr) 2006-03-08

Family

ID=33485268

Family Applications (1)

Application Number Title Priority Date Filing Date
EP04734584A Withdrawn EP1632027A1 (fr) 2003-05-27 2004-05-24 Selecteur de canaux a commande automatique de gain

Country Status (5)

Country Link
EP (1) EP1632027A1 (fr)
JP (1) JP2007500989A (fr)
KR (1) KR20060013554A (fr)
CN (1) CN100546184C (fr)
WO (1) WO2004107574A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4676365B2 (ja) * 2006-03-20 2011-04-27 新日本無線株式会社 利得切換増幅器
KR102211171B1 (ko) * 2020-04-17 2021-02-01 삼성에스디아이 주식회사 이차전지 및 그 케이스 제조방법

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0667712A2 (fr) * 1994-02-14 1995-08-16 Hitachi, Ltd. Récepteur de télévision haute définition
EP0797299A2 (fr) * 1996-03-21 1997-09-24 Nec Corporation Commande de gain automatique
US5940143A (en) * 1995-10-06 1999-08-17 Hitachi, Ltd. High-definition television signal receiving apparatus and gain control circuit thereof
WO2004098052A1 (fr) * 2003-04-29 2004-11-11 Koninklijke Philips Electronics N. V. Circuit recepteur dote d'un gain d'amplificateur a frequence intermediaire reglable

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4172239A (en) * 1978-10-06 1979-10-23 Rca Corporation Signal attenuator
CN1130823A (zh) * 1995-03-06 1996-09-11 郑永裕 具有可变频宽解调电路的卫星接收调谐器
GB9508592D0 (en) * 1995-04-27 1995-06-14 Rca Thomson Licensing Corp Rf filter and agc circuit
JP3627783B2 (ja) * 1996-12-26 2005-03-09 シャープ株式会社 ケーブルモデム用チューナ
CN1190964C (zh) * 2000-02-14 2005-02-23 夏普公司 电缆调制解调器的调谐器

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0667712A2 (fr) * 1994-02-14 1995-08-16 Hitachi, Ltd. Récepteur de télévision haute définition
US5940143A (en) * 1995-10-06 1999-08-17 Hitachi, Ltd. High-definition television signal receiving apparatus and gain control circuit thereof
EP0797299A2 (fr) * 1996-03-21 1997-09-24 Nec Corporation Commande de gain automatique
WO2004098052A1 (fr) * 2003-04-29 2004-11-11 Koninklijke Philips Electronics N. V. Circuit recepteur dote d'un gain d'amplificateur a frequence intermediaire reglable

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of WO2004107574A1 *

Also Published As

Publication number Publication date
CN1795612A (zh) 2006-06-28
WO2004107574A1 (fr) 2004-12-09
CN100546184C (zh) 2009-09-30
KR20060013554A (ko) 2006-02-10
JP2007500989A (ja) 2007-01-18

Similar Documents

Publication Publication Date Title
CN1098558C (zh) 调谐器的自动增益控制电路装置
JP3263395B2 (ja) 利得制御増幅器
KR100193848B1 (ko) 대역확산통신기에 있어서 수신신호 이득 자동제어장치 및 방법
US8624654B2 (en) Automatic step variable attenuator and radio communication device
US3344355A (en) Delayed automatic gain control for transistorized wave signal receivers
RU2124276C1 (ru) Комбинация детектора и частотно-избирательного фильтра
US4393513A (en) Input signal level control device for receiver
JP2002076805A (ja) Ａｇｃ増幅回路及びそれを用いた受信装置
US4761828A (en) Radio receiver
US4403346A (en) AGC System for wide band tuner
US4817198A (en) Radio receiver
US20050221779A1 (en) AGC circuit
CN102045076A (zh) 接收电路及半导体装置
US6903783B2 (en) Tuner for receiving television signal in VHF band and UHF band
EP2043270A2 (fr) Réception de diffusion de télévision numérique
US4792992A (en) Radio receiver
WO2004107574A1 (fr) Selecteur de canaux a commande automatique de gain
US6977555B2 (en) Tuner circuit
US6631171B1 (en) QPSK modulation signal receiving unit
JPH05300043A (ja) アッテネータ回路
US20020191118A1 (en) Compactly-designed television receiver
JP3005472B2 (ja) 受信機
KR100298892B1 (ko) 스위칭트랩기능을구비한디지탈위성방송용튜너
JP2000041199A (ja) 映像中間周波増幅回路
JPH0678241A (ja) 自動利得制御回路

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 20051227

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IT LI LU MC NL PL PT RO SE SI SK TR

DAX Request for extension of the european patent (deleted)
R17C First examination report despatched (corrected)

Effective date: 20060331

17Q First examination report despatched

Effective date: 20060331

RAP1 Party data changed (applicant data changed or rights of an application transferred)

Owner name: NXP B.V.

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 20070703