Auxiliary amplifier selection circuit for a CCD camera

Abstract

Object: To broaden the range of photographing of object, until illumination of 0.02 lux. Construction: In the case of sufficient bright object, photographing is performed by a conventional circuit at a high S/N ratio, at a high degree. In the case of an insufficient bright object, inserting auxiliary amplifying circuit m, m 1 , m 2 or em and ignoring the S/N ratio, and raising the amplification degree. In the case of sufficient bright object, photographing is performed by high S/N ratio, and high degree, in the case of insufficient bright object, an auxiliary amplifying circuit m, m 1 , m 2 or em is inserted ignoring the S/N ratio until utility noise composite of 20 dB (10%).

1. In a signal amplifying circuit system for a charge coupled device camera the improvement comprising; :
 a first automatic gain control auxiliary amplifying circuit (m 1 )  having a low amplification degree and high signal to noise ratio;  
 a second separate automatic gain control auxiliary amplifying circuit (m 2 )  having a high amplification degree and a low signal to noise ratio that is less than about the minimum signal to noise ratio of said auxiliary amplifying circuit with a high signal to noise ratio;  
 a detector for detecting a change of object illumination; and,  
 a switch activated by said detector for switching from said first automatic gain control auxiliary amplifying circuit (m 1 )  having a low amplification degree and a high signal to noise ratio to said second separate automatic gain control auxiliary amplifying circuit (m 2 )  having a high amplification degree and a low signal to noise ratio when said object illumination produces a signal-to-noise ratio that is less than the minimum signal to noise ratio of said first automatic gain control auxiliary amplifying circuit (m 1 )  with said high signal to noise ratio;  
 whereby said charge coupled device camera is switched to said second separate automatic gain control auxiliary amplifying circuit (m 2 )  having a high amplification degree when ambient illumination of said object is extremely low thereby substantially broadening the range of light levels suitable for photographs by said charged coupled device camera.  
 
     
     
       2. The signal amplifying circuit system according to  claim 1  in which said signal to noise ratio of said second separate automatic gain control auxiliary amplifying circuit (m 2 )  with a high amplification degree and low signal to noise ratio is a minimum signal to noise ratio that is greater than about 20 dB. 
     
     
       3. The signal amplifying circuit system according to  claim 2  in which said second separate automatic gain control auxiliary amplifying circuit (m 2 )  having a high signal to noise ratio has a signal to noise ratio that is kept at greater than about 40 dB. 
     
     
       4. The signal amplifying circuit system according to  claim 2  in which said detector is constructed to detect and activate said switch at light levels below about 0.02 lux at a signal to noise ratio above about 40 dB. 
     
     
       5. The signal amplifying circuit system according to  claim 4  in which the light level for photographs are broadened to low light levels in the range of 0.01 lux to about 0.001 lux. 
     
     
       6. A signal amplifying circuit system for a charge coupled device ( CCD )  camera, which inputs an input signal from a charge coupled device  ( CCD )  sensor and outputs a video output signal, comprising:      a first automatic gain control amplifier for amplifying the input signal from a charge coupled device  ( CCD )  sensor, said first automatic gain control amplifier being capable of varying an amplification degree so as to substantially output a constant voltage within a predetermined range of input;        a second automatic gain control amplifier coupled in series with the first automatic gain control amplifier, an amplification degree of said second automatic gain control substantially being  0  dB when the video output signal which is obtained through the first automatic gain control amplifier and the second automatic gain control amplifier is not less than a predetermined level; and        an automatic gain control  ( AGC )  level detector for monitoring the video output signal and for varying the amplification degree of said second automatic gain control amplifier when the video output signal is less than a predetermined level,        wherein the input signal from the charge coupled device sensor is amplified by said first automatic gain control amplifier when the video output signal is not less than the predetermined level, and the input signal from the charge coupled device sensor is amplified by both said first automatic gain control amplifier and said second automatic gain control amplifier when the video output signal is less than the predetermined level thereby substantially broadening a range of light levels suitable for photographs by the charge coupled device camera, and        wherein said level detector comprises a comparator which receives said video output signal, and said second automatic gain control amplifier receives an output of said comparator, said amplification degree of said second automatic gain control amplifier being controlled by said output of said comparator.     
     
     
       7. A signal amplifying circuit system for a charge coupled device ( CCD )  camera, comprising:      a first automatic gain control amplifier for amplifying a signal from a charge coupled device  ( CCD )  sensor, said first automatic gain control amplifier being capable of varying an amplification degree so as to substantially output a constant voltage within a predetermined range of input;        a second automatic gain control amplifier coupled in series with the first automatic gain control amplifier, an amplification degree of said second automatic gain control amplifier substantially being  0  dB when a video output signal is not less than a predetermined level; and        an automatic gain control  ( AGC )  level detector for monitoring said video output signal and for varying the amplification degree of said second automatic gain control amplifier when said video output signal is less than a predetermined level,        wherein said detector controls an amplification of said signal from the charge coupled device sensor by varying the amplification degree of said second automatic gain control amplifier based on whether said video output signal is less than the predetermined level, and        wherein said level detector comprises a comparator which receives said video output signal, and said second automatic gain control amplifier receives an output of said comparator, said amplification degree of said second automatic gain control amplifier being controlled by said output of said comparator.     
     
     
       8. The signal amplifying circuit system of  claim 7 , wherein said detector causes said signal from the charge coupled device sensor to be amplified by said first automatic gain control amplifier when said video output signal is not less than the predetermined level, and causes said signal from the charge coupled device sensor to be amplified by said first and second automatic gain control amplifiers when said video output signal is less than the predetermined level. 
     
     
       9. The signal amplifying circuit system of  claim 7 , further comprising:
   a switch coupled to said second automatic gain control amplifier, said detector controlling said switch to control said amplification.     
     
     
       10. The signal amplifying circuit system of  claim 7 , wherein said detector varies the amplification degree of said second automatic gain control amplifier such that a voltage of said video output signal is maintained at a constant voltage. 
     
     
       11. The signal amplifying circuit system of  claim 7 , further comprising:
   a low pass filter receiving the amplified input signal from the first automatic gain control amplifier, and outputting a filtered signal, said second automatic gain control amplifier amplifying said filtered signal.     
     
     
       12. The signal amplifying circuit system of  claim 11 , wherein said predetermined level comprises a reference voltage, said comparator comparing a voltage of said video output signal to said reference voltage. 
     
     
       13. The signal amplifying circuit system of  claim 12 , wherein when said voltage of said video output signal is less than said reference voltage, said output of said comparator causes a change in said amplification degree of said second automatic gain control amplifier. 
     
     
       14. The signal amplifying circuit system of  claim 6 , wherein a signal from the charge coupled device sensor is not amplified by said second automatic gain control amplifier when a video output signal not less than the predetermined level. 
     
     
       15. The signal amplifying circuit system of  claim 12 , wherein if said detector detects that said voltage of said video output signal is less than said reference voltage, said output of said comparator increases said amplification degree of said second automatic gain control amplifier.