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US 6,307,196 B1Granted
Detection circuit having a variable impedance circuit
AssigneeTelefonaktiebolaget LM Ericsson (publ)
InventorsJohn Thompson, Raymond Filippi, Joakim Bängs
Life of this patent
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Abstract
A photodiode detection circuit using a transimpedance amplifier circuit is disclosed. Overload current from the photodiode is diverted away from the amplifier to a voltage supply, e.g. ground, through an overload protection diode connected in series with the photodiode. A differential structure is also disclosed.
Claims16
A detection circuit, comprising:
- a photodiode, which draws a current which depends on the intensity of a light signal incident thereon;
- a variable impedance circuit connected in series with the photodiode, and being connected to the photodiode at a connection node, the impedance of the variable impedance circuit depending on the current therethrough;
- a transimpedance amplifier circuit, including a transimpedance amplifier and a feedback circuit, and having an input and an output, the transimpedance amplifier circuit input being connected to the connection node, and the transimpedance amplifier circuit output forming a detection circuit output;
- the series connection of the variable impedance circuit and the photodiode being connected between a pair of voltage supply rails by a connection having a low impedance at AC and DC, wherein
- the input impedance of the transimpedance amplifier circuit matches the impedance of the variable impedance circuit at a cutoff current, and is high compared to the impedance of the variable impedance circuit at an overload current.
2 more elements
A detection circuit, comprising:
- a photodiode, which draws a current which depends on the intensity of a light signal incident thereon, the photodiode being connected between first and second connection nodes;
- a first variable impedance circuit connected between the first connection node and a first voltage supply rail by a connection having a low impedance at AC and DC;
- a second variable impedance circuit connected between the second connection node and a second voltage supply rail by a connection having a low impedance at AC and DC;
- and
- a differential transimpedance amplifier circuit, including first and second transimpedance amplifier circuits each having an input and an output, the first transimpedance amplifier circuit input being connected through a first capacitor to the first connection node, the second transimpedance amplifier circuit input being connected through a second capacitor to the second connection node, and the first and second transimpedance amplifier circuit outputs forming inputs to a differential amplifier to provide a detection circuit output;
- the input impedances of the transimpedance amplifier circuits being high compared to the impedance of the variable impedance circuits at an overload current.
3 more elements
A detection circuit, comprising:
- a photodiode, which draws a current which depends on the intensity of a light signal incident thereon, the photodiode being connected between first and second connection nodes;
- a first variable impedance circuit connected between the first connection node and a first voltage supply rail by a connection having a low impedance at AC and DC, the impedance of the first variable impedance circuit depending on the current therethrough;
- a second variable impedance circuit connected between the second connection node and a second voltage supply rail by a connection having a low impedance at AC and DC, the impedance of the second variable impedance circuit depending on the current therethrough;
- and
- a differential transimpedance amplifier circuit, including first and second transimpedance amplifier circuits each having an input and an output, the first transimpedance amplifier circuit input being connected through a first capacitor to the first connection node, the second transimpedance amplifier circuit input being connected through a second capacitor to the second connection node, and the first and second transimpedance amplifier circuit outputs forming inputs to a differential amplifier to provide a detection circuit output;
- wherein
- the input impedances of the transimpedance amplifier circuits match the impedances of the variable impedance circuits at a cutoff current, and are high compared to the impedances of the variable impedance circuits at an overload current.
4 more elements
Dependencies are inferred from the claim text.