Detector for short wave fiber optic communications with compensation to reduce detector jitter
View Patent ↗A detector is provided for short wave fiber optic communication having compensation to reduce detector jitter. The detector includes a photodetector providing a modulated current. A transimpedance amplifier is coupled to the photodetector receiving the modulated current and providing an output voltage signal. An output buffer is coupled to the transimpedance amplifier receiving the output voltage signal. The output buffer includes a differential transistor pair; a pair of source degeneration resistors connected to the differential transistor pair; and a capacitor coupled between connections of the differential transistor pair and the source degeneration resistors. The value of the capacitor coupled between connections of the differential transistor pair and the source degeneration resistors is selected to reduce jitter. The capacitor passes high slew rate transimpedance amplifier output voltage signals more readily than low slew rate transimpedance amplifier output voltage signals. The effect of the capacitor is to bypass the gain limiting effects of the source degeneration resistors. As a result the differential transistor pair accentuates high slew rates over lower ones so that detector jitter is reduced.
1. A detector for short wave fiber optic communications having compensation to reduce detector jitter comprising:
a photodetector for providing a modulated current;
a transimpedance amplifier coupled to said photodetector receiving said modulated current and providing an output voltage signal;
an output buffer coupled to said transimpedance amplifier receiving said output voltage signal; and
said output buffer including a differential transistor pair; said transimpedance amplifier output voltage signal applied to said differential transistor pair; a pair of source degeneration resistors connected to said differential transistor pair; and a capacitor coupled between connections of said differential transistor pair and said source degeneration resistors; said capacitor having a selected value for reducing detector jitter.
2. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 1 wherein said differential transistor pair is a high gain amplifier and is responsive to said applied transimpedance amplifier output voltage signal for accentuating high slew rates over lower slew rates.
3. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 1 wherein said capacitor passes high slew rate transimpedance amplifier output voltage signals and limits low slew rate transimpedance amplifier output voltage signals.
4. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 1 wherein said photodetector includes a lateral photodetector structure.
5. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 1 includes a current source and a current sink for biasing said photodetector.
6. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 1 wherein said transimpedance amplifier output voltage signal applied to said differential transistor pair is a differential output voltage signal and said output buffer providing a differential detector voltage signal.
7. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 1 wherein said pair of source degeneration resistors connected to said differential transistor pair control gain of said differential transistor pair.
8. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 1 wherein said output buffer includes a pair of drain load resistors connected between said differential transistor pair and a high power supply voltage.
9. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 1 wherein said differential transistor pair is formed by a pair of metal semiconductor field effect transistors (MESFETs).
10. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 1 further includes AC coupling capacitors coupled between said photodetector and said transimpedance amplifier.
11. A detector for short wave fiber optic communications having compensation to reduce detector jitter comprising:
a lateral photodetector biased by a current source and a current sink for providing a modulated current signal;
a transimpedance amplifier coupled to said lateral photodetector receiving said modulated current signal and providing a differential output voltage signal;
an output buffer coupled to said transimpedance amplifier receiving said differential output voltage signal; and
said output buffer including a differential transistor pair; said differential output voltage signal of said transimpedance amplifier applied to said differential transistor pair; a pair of source degeneration resistors connected to said differential transistor pair; and a capacitor coupled between connections of said differential transistor pair and said source degeneration resistors; said capacitor having a selected value to reduce detector jitter; and said capacitor passing high slew rate signals and limiting low slew rate signals.
12. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 11 wherein said differential transistor pair is a high gain amplifier and is responsive to said applied differential output voltage signal for accentuating high slew rates over lower slew rates.
13. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 11 wherein said output buffer includes a pair of drain load resistors connected between said differential transistor pair and a high power supply voltage.
14. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 11 wherein said output buffer includes a current source connected between said pair of source degeneration resistors and ground.
15. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 11 wherein said differential transistor pair is formed by a pair of high gain metal semiconductor field effect transistors (MESFETs).
16. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 11 wherein said output buffer includes a unity gain source follower amplifier coupled to said differential transistor pair.
17. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 11 wherein said output buffer includes a current reference source and a current source coupled to said current reference source and connected between said pair of source degeneration resistors and ground.
18. A detector for short wave fiber optic communications having compensation to reduce detector jitter as recited in claim 11 includes AC coupling capacitors coupled between said lateral photodetector and said transimpedance amplifier; said AC coupling capacitors for passing predefined frequency modulated current signals and blocking low frequency modulated current signals.
19. A buffer circuit for a signal detector having compensation to reduce detector jitter comprising:
a differential transistor pair;
a voltage signal applied to said differential transistor pair;
a pair of source degeneration resistors connected to said differential transistor pair; and
a capacitor coupled between connections of said differential transistor pair and said source degeneration resistors; said capacitor having a selected value for reducing detector jitter.
20. A buffer circuit for a signal detector having compensation to reduce detector jitter as recited in claim 19 wherein said differential transistor pair is formed by a pair of high gain metal semiconductor field effect transistors (MESFETs).