Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03G—CONTROL OF AMPLIFICATION
  • H03G3/00—Gain control in amplifiers or frequency changers
  • H03G3/005—Control by a pilot signal
• • 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

Definitions

• the present invention relates to an automatic gain control circuit in a
• the instant invention is directed to an automatic gain
• control circuit in a cascaded telecommunication system having a circuit that takes over control of the gain of the automatic gain control circuit when a reference carrier, normally used to control the gain, is lost or falls below a predetermined threshold level.
• the telecommunication system e.g. , a twisted pair, a coaxial cable, or an optical filter
• Telecommunication systems typically employ a large number of items of equipment
• the useful signal in a transmission link may be
• cable attenuation also varies with temperature. Many other factors may be
• AGC AGC amplifier
• pilot signal At receiving stations, or signal-repeating stations, or other distribution points along the telecommunication signal distribution system, the pilot signal is extracted and measured. A signal, representative of the difference between the
• amplitude of the received pilot signal and a predetermined reference level is used to control the gain of the amplifier to keep the gain of the system at a given, relatively constant, level. Accordingly, as the carrier varies, the gain and slope of the amplifier will vary in proportion.
• pilot signals to determine gain for a given automatic gain control circuit. For example, if there is a loss of pilot signal, or the level of the pilot becomes too low for detection, the gain levels will tend to maximize with a risk of saturating components located downstream of the detected
• the present invention provides an improved automatic gain control method
• the present invention provides a signal that approximates the attenuation of a given
• the transmission medium based on the temperature of the housing in which the automatic gain control circuit is located.
• control element of the system will generate an approximated signal based on a temperature
• pilot signal is redetected.
• the automatic gain control circuit monitors for the presence of the pilot carrier. If the pilot carrier level falls below a predetermined threshold,
• the automatic gain control circuit will automatically switch the input of the gain control
• circuit of the gain control element e.g. , a Bode circuit, which dynamically controls the gain
• the gain setting will, therefore, be based on an
• Another object of the present invention is to provide a thermal control circuit that
• Yet another object of the present invention is to provide automatic switching between
• the thermal circuit and the received pilot signal based on the signal level of the received pilot
• an automatic gain control circuit including: a gain element controlling
• a gain of the automatic gain control circuit a detector for detecting a pilot signal; a comparator
• the switch is activated when the output of the comparator indicates that a level of the
• thermal circuit connected to the gain control element via the switch, the thermal circuit providing a signal representing the temperature of a housing in which the automatic gain
• the gain control circuit is disposed, the gain control circuit providing an attenuation characteristic of
• the signal provided by the thermal circuit is used by the gain element in place of the pilot
• the gain control element controlling a gain of the automatic gain control circuit based on a
• Attenuation approximation signal representing an approximation of attenuation of the
• FIG. 1 is a block diagram of an AGC portion of a telecommunication distribution
• FIG. 2 is a schematic diagram of details of a preferred embodiment of the present
• FIG. 3 is a flow chart representing the steps of the preferred embodiment of the
• AGC automatic gain control
• the pilot signal portion of the received signal is received at the input to the amplifier 5.
• Bode circuit 7 acts as the gain control element of the automatic
• Bode circuits are well known to those skilled in the art. Typically, a
• Bode circuit is a tilt network that simulates cable performance over temperature variation, e.g. ,
• the pivot point of a Bode circuit is usually
• the Bode circuit 7 drives a second amplification stage 11 that provides an output signal having a level adjusted in accordance with the parameters of the system, i.e. , either a
• the optional status monitor 13 may also receive a signal 12 from the thermal circuit
• the status monitor 13 may then
• the thermal control circuit 2 monitors for the presence of a pilot signal.
• a band-pass filter 30 receives
• the pass band of the band pass filter 30 is chosen such that it passes
• the thermal circuit 2 includes a detector 17, typically
• the detector 17 is amplified by a DC amplifier 19 and transmitted to a DC switch 21.
• the pilot signal is also transmitted from the detector 17 to a comparator 25.
• comparator 25 compares the pilot signal level to a predetermined reference level, V ⁇ f , selected
• a switch driver 27 is activated and provides a signal to the DC switch 21 , causing
• thermal circuit 29 is a temperature-sensing circuit, typically
• thermistor that produces a voltage proportional to the housing temperature of the
• Bode circuit 29 is directed to the Bode circuit 7 via the switch 21 and the Bode driver 23.
• Bode circuit 7 provides an approximation of signal attenuation over temperature of a given
• Bode circuit 7 bases its
• the automatic gain control circuit may optionally include a manual switch 31 that can
• the manual switch 31 allows arbitrary switching
• Figure 3 is a flow diagram outlining the
• the sampled output from the main amplifier output is attenuated and
• a DC amplifier 19 is used
• Temperature-sensing circuit 29 produces a voltage proportional to the housing temperature at
• Comparator 25 compares the detected level of the pilot signal at point 6 with a
• the manual switch 31 at point 12 is for testing and alignment purposes.
• the signal at point 12 is applied to the Bode driver 23 to provide the current necessary to drive
• the system monitors the input signal for
• pilot signal is then compared to an arbitrary reference
• the pilot is either missing or has been attenuated to an unacceptably low level. If the
• pilot signal level is greater than the reference level, the pilot signal is used to drive the Bode
• comparator 25 causes the switch driver 27 to signal the DC switch 21 , thus causing the switch
• Bode circuit 7 provides a signal having an attenuation based on a temperature of the housing
• the approximation signal is used by

Landscapes

• Control Of Amplification And Gain Control (AREA)
• Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=24613669

Family Applications (1)

Country Status (7)

Families Citing this family (1)

Citations (2)

Family Cites Families (20)

• 1996
  • 1996-05-31 US US08/651,651 patent/US5742202A/en not_active Expired - Lifetime
• 1997
  • 1997-05-30 EP EP97926820A patent/EP0903010B1/en not_active Expired - Lifetime
  • 1997-05-30 AU AU31495/97A patent/AU3149597A/en not_active Abandoned
  • 1997-05-30 ES ES97926820T patent/ES2151278T3/es not_active Expired - Lifetime
  • 1997-05-30 WO PCT/US1997/009233 patent/WO1997045953A1/en active IP Right Grant
  • 1997-05-30 BR BR9709377A patent/BR9709377A/pt not_active IP Right Cessation
  • 1997-05-30 DE DE69702520T patent/DE69702520T2/de not_active Expired - Fee Related

Patent Citations (2)

Non-Patent Citations (1)

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