Process and temperature-compensated transimpedance amplifier
View Patent ↗An optical receiver is disclosed that exhibits an improved phase margin and substantially constant output in response to changes in operating conditions (e.g., temperature, process, etc.). In accordance with the illustrative embodiment, a common-mode feedback comparison is performed prior to conversion of the signal from single-ended to differential voltage. When the common-mode feedback comparison is performed in this way, there are fewer amplifiers in the signal path and the phase margin of the common-mode feedback loop is increased. In addition, as the common-mode feedback is performed at the first stage of the transimpedance amplifier, the gain response of the transimpedance amplifier remains substantially constant in response to changes in temperature, input current range, and for different integrated circuit fabrication processes.
1. An apparatus comprising:
(1) an amplification stage comprising a first input, a second input, a first output, and a second output;
(2) a feedback network comprising an input, a first output, and a second output;
wherein said first input of said amplification stage is also said input of said feedback network; and
wherein said second input of said amplification stage is said second output of said feedback network;
(3) a transimpedance stage comprising a signal input, a bias input, and an output;
wherein said bias input of transimpedance stage is based on first output of said feedback network;
wherein said first input of said amplification stage is based on said output of said transimpedance stage; and
wherein said input of said feedback network is based on said output of said transimpedance stage;
wherein said transimpedance stage comprises:
(a) a first transistor comprising a gate, a drain, a source, and
(b) a second transistor comprising a gate, a drain, and a source;
wherein said gate of said first transistor is electrically connected to said signal input of said transimpedance stage;
wherein said gate of said second transistor is electrically connected to said bias input of said transimpedance stage;
wherein said source of said first transistor is electrically connected to a common voltage;
wherein said source of said second transistor is electrically connected to a common voltage; and
wherein said gate of said first transistor is electrically connected to said drain of said second transistor.
2. The apparatus of claim 1 wherein said transimpedance stage further comprises:
(c) a third transistor comprising a gate, a drain, and a source;
wherein said gate of said third transistor is electrically connected to said drain of said first transistor;
wherein said source of said third transistor is electrically connected to said drain of said second transistor; and
wherein said drain of said third transistor is electrically connected to said first input of said amplification stage.
3. An apparatus comprising:
(1) an amplification stage comprising a first input, a second input, a first output, and a second output;
(2) a feedback network comprising an input, a first output, and a second output;
wherein said first input of said amplification stage is also said input of said feedback network; and
wherein said second input of said amplification stage is said second output of said feedback network;
(3) a transimpedance stage comprising a signal input, a bias input, and an output;
wherein said bias input of transimpedance stage is based on first output of said feedback network;
wherein said first input of said amplification stage is based on said output of said transimpedance stage; and
wherein said input of said feedback network is based on said output of said transimpedance stage;
wherein said transimpedance stage comprises:
(a) a first transistor comprising a gate, a drain, and a source; and
(b) a second transistor comprising a gate, a drain, and a source;
wherein said drain of said first transistor is electrically connected to said signal input of said transimpedance stage;
wherein said gate of said first transistor is electrically connected to said bias input of said transimpedance stage;
wherein said drain of said first transistor is electrically connected to said source of said second transistor; and
wherein said drain of said second transistor is electrically connected to said first input of said amplification stage.
4. An apparatus comprising:
(1) an amplification stage comprising a first input, a second input, a first output, and a second output;
(2) a feedback network comprising an input, a first output, and a second output;
wherein said first input of said amplification stage is also said input of said feedback network; and
wherein said second input of said amplification stage is said second output of said feedback network;
(3) a transimpedance stage comprising a signal input, a bias input, and an output;
wherein said bias input of transimpedance stage is based on first output of said feedback network;
wherein said first input of said amplification stage is based on said output of said transimpedance stage; and
wherein said input of said feedback network is based on said output of said transimpedance stage;
wherein said transimpedance stage comprises:
(a) a transistor comprising a gate, a drain, and a source;
(b) a first resistor comprising a first terminal and a second terminal; and
(c) a second resistor comprising a first terminal and a second terminal;
wherein said gate of said transistor is electrically connected to said first terminal of said first resistor;
wherein said drain of said transistor is electrically connected to said first terminal of said second resistor;
wherein said drain of said transistor is electrically connected to said first input of said amplification stage;
wherein said source of said transistor is electrically connected to said signal input of said transimpedance stage;
wherein said second terminal of said first resistor is electrically connected to a voltage supply; and
wherein said second terminal of said second resistor is electrically connected to said voltage supply.