Automatic gain control circuit for selectively providing an accurate linearity or a broad bandwidth

An automatic gain control circuit which is selectively set to a state where an output from said automatic gain control circuit has an accurate linearity or a state where said automatic control unit has a broad bandwidth with respect to inputs thereto, said automatic gain control circuit comprising:

• a first input unit converting a first input current into a first voltage, a bandwidth of said first input unit being variable;
• a second input unit converting a second input current into a second voltage, a bandwidth of said second input unit being variable;
• a third input unit converting a third input current into a third voltage, a bandwidth of said third input unit being variable;
• a fourth input unit converting a fourth input current into a fourth voltage, a bandwidth of said fourth input unit being variable;
• a main variable constant current source generating first, second, third and fourth constant currents, said first constant current flowing from said first input unit to said main variable constant current source, said second constant current flowing from said second input unit to said main variable constant current source, said third constant current flowing from said third input unit to said main variable constant current source, said fourth constant current flowing from said fourth input unit to said variable constant current source, said first, second, third and fourth constant currents being varied by a control signal supplied by an external signal source so that the bandwidths of said first, second, third and fourth input units are varied:
• a first automatic gain control output calculating unit calculating a first output based on said first voltage and said fourth voltage;
• and
• a second automatic gain control output calculating unit calculating a second output based on said second voltage and said third voltage.