US5521555A — Ultra low noise optical receiver

Claim 1

Independent Claim 240 words

An optical receiver for receiving an incident optical signal and producing an electrical signal indicative of the optical signal intensity, comprising: a photodetector for receiving the optical signal and producing a photodetector output signal that is indicative of the intensity of the optical signal; an ultra low capacitance differential input stage connected to receive the photodetector output signal and producing a buffer output signal; and an operational amplifier having low noise and ultra-wide bandwidth connected to the ultra low capacitance differential input stage to receive the buffer output signal therefrom as a driving signal, the low noise ultra-wide bandwidth operational amplifier producing a low noise output signal; the ultra low capacitance differential input stage comprising: a first amplifier circuit comprising: a first transistor connected to and being bootstrapped by the photodetector, the first transistor acting as a first gain buffer having low noise, low capacitance and unity gain; a second transistor configured as a first voltage follower connected between the output of the first buffer and the operational amplifier to isolate the output of the first buffer from parasitic capacitive loading from a biasing network; a second amplifier circuit comprising: a third transistor having an input connected to a reference potential, the third transistor acting as a second gain buffer having low noise, low capacitance and unity gain; and a fourth transistor configured as a second voltage follower connected between the output of the second buffer and the operational amplifier.

Claim 2

Dependent Claim 240 words

An optical receiver for receiving an incident optical signal and producing an electrical signal indicative of the optical signal intensity, comprising: a photodetector for receiving the optical signal and producing a photodetector output signal that is indicative of the intensity of the optical signal; an ultra low capacitance differential input stage connected to receive the photodetector output signal and producing a buffer output signal; and an operational amplifier having low noise and ultra-wide bandwidth connected to the ultra low capacitance differential input stage to receive the buffer output signal therefrom as a driving signal, the low noise ultra-wide bandwidth operational amplifier producing a low noise output signal; the ultra low capacitance differential input stage comprising: a first amplifier circuit comprising: a first transistor connected to and being bootstrapped by the photodetector, the first transistor acting as a first gain buffer having low noise, low capacitance and unity gain; a second transistor configured as a first voltage follower connected between the output of the first buffer and the operational amplifier to isolate the output of the first buffer from parasitic capacitive loading from a biasing network; a second amplifier circuit comprising: a third transistor having an input connected to a reference potential, the third transistor acting as a second gain buffer having low noise, low capacitance and unity gain; and a fourth transistor configured as a second voltage follower connected between the output of the second buffer and the operational amplifier.

Claim 3

Dependent Claim 43 words

The optical receiver of claim 1, further including a first resistor connected to the output of the first buffer and a second resistor connected to the output of the second buffer to isolate the first and second buffers, respectively, from parasitic capacitive loading.

Claim 4

Dependent Claim 32 words

The optical receiver of claim 1, further including an RC network connected between an input and the output of the operational amplifier to provide a lead-lag network in the open loop gains.

Claim 5

Dependent Claim 41 words

The optical receiver of claim 1, further comprising a transimpedance network connected between the output of the operational amplifier and a terminal of the photodetector for generating a high transimpedance bandwidth and for reducing high frequency noise in the output signal.

Claim 6

Dependent Claim 49 words

The optical receiver of claim 1, further including a first bootstrapping capacitor connected between an input of the first buffer and the output of the first voltage follower and a second bootstrapping capacitor connected between the input of the second buffer and the output of the second voltage follower.

Claim 7

Dependent Claim 14 words

The optical receiver of claim 1 wherein the first and third transistors are JFETS.

Claim 8

Dependent Claim 16 words

The optical receiver of claim 1 wherein the second and fourth transistors are bipolar junction transistors.

Claim 9

Dependent Claim 179 words

The optical receiver of claim 1, wherein: the first transistor comprises a first JFET having a gate, a source and a drain, the photodetector being connected between the gate and source of the first JFET; the second transistor comprises a first bipolar junction transistor having an emitter, a collector and a base, the base of the first bipolar junction transistor being connected to the source of the first JFET and to the photodetector, the emitter of the first bipolar junction transistor being connected to a first input of the operational amplifier; the third transistor comprises a second JFET having a gate, a source and a drain; and the fourth transistor comprises a second bipolar junction transistor having an emitter, a collector and a base, the collector of the second bipolar junction transistor being connected to the collector of the first bipolar junction transistor, the emitter of the second bipolar junction transistor being connected to a second input of the operational amplifier, and the base of the second bipolar junction transistor being connected to the source of the second JFET.

Claim 10

Dependent Claim 43 words

The optical receiver of claim 8, further including a first resistor connected to the output of the first buffer and a second resistor connected to the output of the second buffer to isolate the first and second buffers, respectively, from parasitic capacitive loading.

Claim 11

Dependent Claim 32 words

The optical receiver of claim 8, further including an RC network connected between an input and the output of the operational amplifier to provide a lead-lag network in the open loop gains.

Claim 12

Dependent Claim 41 words

The optical receiver of claim 8, further comprising a transimpedance network connected between the output of the operational amplifier and the anode of the photodiode for generating a high transimpedance bandwidth and for reducing high frequency noise in the output signal.

Claim 13

Dependent Claim 51 words

The optical receiver of claim 8, further including a first bootstrapping capacitor connected between the drain of the first JFET and the emitter of the first bipolar junction transistor and a second bootstrapping capacitor connected between the drain of the second JFET and the emitter of the second bipolar junction transistor.

Claim 14

Dependent Claim 154 words

An optical receiver for receiving an incident optical signal and producing an electrical signal indicative of the optical signal intensity, comprising: a photodetector for receiving the optical signal and producing a photodetector output signal that is indicative of the intensity of the optical signal; a first low noise, wide band width, low capacitance JFET connected by the gate and source thereof to the photodetector as a follower to receive the photodetector output signal; a first low noise, low capacitance bipolar junction transistor connected as an emitter follower to the first JFET; a second low noise, wide bandwidth, low capacitance JFET connected as a reference follower; a second low noise, low capacitance bipolar transistor connected to the second JFET such that the second bipolar junction transistor is connected as an emitter follower to the second JFET; and an operational amplifier having low noise and ultra-wide bandwidth connected to the emitters of the bipolar junction transistor.

Claim 15

Dependent Claim 154 words

An optical receiver for receiving an incident optical signal and producing an electrical signal indicative of the optical signal intensity, comprising: a photodetector for receiving the optical signal and producing a photodetector output signal that is indicative of the intensity of the optical signal; a first low noise, wide band width, low capacitance JFET connected by the gate and source thereof to the photodetector as a follower to receive the photodetector output signal; a first low noise, low capacitance bipolar junction transistor connected as an emitter follower to the first JFET; a second low noise, wide bandwidth, low capacitance JFET connected as a reference follower; a second low noise, low capacitance bipolar transistor connected to the second JFET such that the second bipolar junction transistor is connected as an emitter follower to the second JFET; and an operational amplifier having low noise and ultra-wide bandwidth connected to the emitters of the bipolar junction transistor.

Claim 16

Independent Claim 257 words

A method for forming an ultra-low noise optical receiver for receiving an incident optical signal and producing an electrical signal indicative of the optical signal intensity, comprising the steps of: arranging a photodetector to receive the optical signal and produce a photodetector output signal that is indicative of the intensity of the optical signal; forming an ultra low capacitance differential input stage to receive the photodetector output signal and to produce a buffer output signal; and connecting an operational amplifier having low noise and ultra-wide bandwidth to the ultra low capacitance differential input stage to receive the buffer output signal therefrom as a driving signal and produce a low noise output signal; the step of forming the ultra low capacitance differential input stage comprises the steps of: forming a first amplifier circuit by the steps of: connecting a first transistor in a bootstrap relationship to the photodetector such that the first transistor acting as a first buffer having low noise, low capacitance and unity gain; connecting a second transistor configured as a first voltage follower between the output of the first buffer and the operational amplifier to isolate the output of the first buffer from loading of at least the operational amplifier; forming a second amplifier circuit by the steps of: connecting a third transistor to a reference potential, the third transistor acting as a second buffer having low noise, low capacitance and unity gain; and connecting a fourth transistor configured as a second voltage follower between the output of the second buffer and the operational amplifier.

Claim 17

Independent Claim 257 words

A method for forming an ultra-low noise optical receiver for receiving an incident optical signal and producing an electrical signal indicative of the optical signal intensity, comprising the steps of: arranging a photodetector to receive the optical signal and produce a photodetector output signal that is indicative of the intensity of the optical signal; forming an ultra low capacitance differential input stage to receive the photodetector output signal and to produce a buffer output signal; and connecting an operational amplifier having low noise and ultra-wide bandwidth to the ultra low capacitance differential input stage to receive the buffer output signal therefrom as a driving signal and produce a low noise output signal; the step of forming the ultra low capacitance differential input stage comprises the steps of: forming a first amplifier circuit by the steps of: connecting a first transistor in a bootstrap relationship to the photodetector such that the first transistor acting as a first buffer having low noise, low capacitance and unity gain; connecting a second transistor configured as a first voltage follower between the output of the first buffer and the operational amplifier to isolate the output of the first buffer from loading of at least the operational amplifier; forming a second amplifier circuit by the steps of: connecting a third transistor to a reference potential, the third transistor acting as a second buffer having low noise, low capacitance and unity gain; and connecting a fourth transistor configured as a second voltage follower between the output of the second buffer and the operational amplifier.

Claim 18

Dependent Claim 46 words

The method of claim 14, further including the steps of; connecting a first resistor to the output of the first buffer; and connecting a second resistor connected to the output of the second buffer to isolate the first and second buffers, respectively, from parasitic capacitive loading.

Claim 19

Dependent Claim 34 words

The method of claim 14, further including the step of connecting an RC network between an input and the output of the operational amplifier to provide a lead-lag network in the open loop gains.

Claim 20

Dependent Claim 43 words

The method of claim 14, further comprising the step of connecting a transimpedance network between the output of the operational amplifier and a terminal of the photodetector for generating a high transimpedance bandwidth and for reducing high frequency noise in the output signal.

Claim 21

Dependent Claim 52 words

The method of claim 14, further including the steps of: connecting a first bootstrapping capacitor between an input of the first buffer and the output of the first voltage follower; and connecting a second bootstrapping capacitor connected between the input of the second buffer and the output of the second voltage follower.

Claim 22

Dependent Claim 215 words

The method of claim 14, wherein: the step of connecting a first transistor comprises the step of connecting a first JFET having a gate connected to a terminal of the photodetector, a source connected to another terminal of the photodetector, and a drain; the step of connecting a second transistor comprises the step of connecting a first bipolar junction transistor having an emitter, a collector and a base, the base of the first bipolar junction transistor being connected to the source of the first JFET and to the photodetector, the emitter of the first bipolar junction transistor being connected to a first input of the operational amplifier; the step of connecting a third transistor comprises the step of connecting a second JFET having a gate, a source and a drain connected to a reference voltage; the step of connecting a fourth transistor comprises the step of connecting a second bipolar junction transistor having an emitter, a collector and a base, the collector of the second bipolar junction transistor being connected to the collector of the first bipolar junction transistor, the emitter of the second bipolar junction transistor being connected to the second input of the operational amplifier, and the base of the second bipolar junction transistor being connected to the source of the second JFET.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1999-05-28	1999-11-27	2000-05-28	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2003-05-28	2003-11-27	2004-05-28	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2007-05-28	2007-11-27	2008-05-28	$7700.00	Window Closed / Lapsed

Ultra low noise optical receiver

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