PULSE-TO-PULSE INSTANTANEOUS AUTOMATIC GAIN CONTROL CIRCUIT

• US 3,704,421 A
• Filed: 12/31/1970
• Issued: 11/28/1972
• Est. Priority Date: 12/31/1970
• Status: Expired due to Term

• Current Assignee: Sp-Marine Incorporated
• Original Assignee: Henry R. Blane
• Inventors: Blane, Henry R.
• Primary Examiner(s): Richardson, Robert L.
• Assistant Examiner(s): Weinstein, Kenneth W.
• Application Number:
  US05/103,083
• Time in Patent Office: 698 Days
• Field of Search: 330/29,85,139 343/5 325/400,408,409,410,411
• US Class Current: 375/345
• CPC Class Codes: G01S 7/34 Gain of receiver varied automatically during pulse-recurrence period, e.g. anti-clutter gain control
• CPC Class Codes: H03G 3/3052 in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver H03G3/32, H03G3/34 take precedence

Abstract

The output signal of an intermediate frequency amplifier is applied to a load through a video detector. An operational amplifier is arranged in a feedback loop so that the signal from the operational amplifier is used to control the gain of the intermediate frequency amplifier. A d.c. bias voltage is applied to the operational amplifier so that the gain control signal applied to the intermediate frequency amplifier represents the combination of the bias voltage and the instantaneous voltage from the video detector. The bias voltage is adjusted so that the intermediate frequency amplifier produces maximum gain so long as the voltage from the video detector remains below a specified value and reduced gain whenever the voltage from the detector exceeds the specified value.

Claims

1. An instantaneous automatic gain control circuit comprising an intermediate frequency amplifier, first means in said intermediate frequency amplifier for receiviNg an input signal, second means in said intermediate frequency amplifier for controlling the gain thereof in response to a control signal, detection means for extracting the modulation envelope of input signals applied to said intermediate frequency amplifier, an operational amplifier connected in feedback relationship so as to provide a control signal to said second means in response to a signal from said detection means, means to bias said operational amplifier to a d.c. level so that the instantaneous value of the control signal applied to said second means is equivalent to the sum of the bias and the amplitude of the signal from said detection means at that instant, said bias means being adjusted so that the signal from said operational amplifier will reduce the gain of said intermediate frequency amplifier whenever the amplitude of the signal from said detection means exceeds a predetermined level, and output means for coupling the output of said detection means to external utilization apparatus.

2. The circuit of claim 1 wherein the input signals to be received are amplitude modulated pulses of relatively short duration, wherein said detection means produces corresponding pulses of a given polarity, said polarity being the same as the polarity of the bias applied to said operational amplifier, and wherein said operational amplifier has a sufficiently short response time so that said control signal pulse occurs entirely during the reception of the corresponding amplitude modulated pulse.

3. The circuit of claim 2 wherein said second means in the intermediate frequency amplifier is characterized in that the amplifier provides maximum gain whenever the applied control signal is below a given minimum level and reduced gain whenever the applied control signal exceeds the minimum level.

4. The circuit of claim 3 wherein the intermediate frequency amplifier is a cascade amplifier connected in differential configuration and arranged so that the signal to be amplified is representative of the difference between the instantaneous voltages applied to said first and second means.

5. The circuit of claim 4 further including first resistance means for resistively coupling signals from said detection means to said operational amplifier, and second resistance means shunting said operational amplifier, said first and second resistance means being proportioned to provide the desired operational amplifier gain, said circuit further including a third resistance means and a switch for optionally connecting said operational amplifier to a bias source, said second and third resistance means being proportioned to provide the desired d.c. level for the control voltage, said circuit still further including a pair of resistors connected serially across the output of said operational amplifier, the junction point between said pair of resistors being connected directly to said second means in said intermediate frequency amplifier.