Automatic gain control method and circuit for use in burst-mode transimpedance amplifier

An automatic gain control circuit for a burst-mode transimpedance amplifier, comprising a transimpedance amplifier, a common-source amplifier, and a transistor;

• wherein the transistor is connected in parallel with a feedback resistor of the transimpedance amplifier, a drain of the transistor is connected to an input terminal Iin of the transimpedance amplifier, a source of the transistor is connected to an output terminal Vout of the transimpedance amplifier;
• an input terminal of the common-source amplifier is connected to the output terminal Vout of the transimpedance amplifier, an output terminal of the common-source amplifier is connected to a gate of the transistor;
• when an input current of the transimpedance amplifier is zero, the transistor is turned off;
• when the input current of the transimpedance amplifier is gradually increased, an output voltage of the transimpedance amplifier is gradually decreased, and an output voltage of the common-source amplifier gradually rises, so that a gate-source voltage of the transistor is gradually increased;
• when the gate-source voltage of the transistor increases to exceed Vth, the transistor is turned on, and an equivalent resistance of the transistor and the feedback resistor decreases, so that the output voltage of the transimpedance amplifier no longer continues to decrease as the input current increases;
• wherein the common-source amplifier includes an NMOS transistor (M2) and a resistor (R1);
• a gate of the NMOS transistor (M2) serves as the input terminal of the common-source amplifier, a drain of the NMOS transistor (M2) serves as the output terminal of the common-source amplifier;
• and the resistor (R1) is connected between the drain of the NMOS transistor (M2) and a power supply voltage Vdd.