40
votes
Accepted
Is it possible to generate light with an antenna?
Photonics is a thing, and it very much treats light as electromagnetic waves in waveguides on silicon, with mixers, delay lines, matching circuits, amplifiers etc as you'd do for a RFIC.
Just as an ...
- 94.9k
38
votes
How does a 40 Gbit/s Ethernet interface process packets in silicon?
40G Ethernet is really four physical 10G links running in parallel. Modern FPGAs have SERDES hardware that can run at well over 10 Gbps, and it's common to use four 32-bit buses running at 312.5 MHz ...
- 173k
27
votes
Accepted
How does a 4 pin RGB connector work without ground?
This is how it looks on the driver end. Whatever channel you want to drive, the R, G and/or B becomes ground with the help of a transistor, completing the circuit and allowing current to flow.
...
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24
votes
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What is the purpose of using an analog optocoupler?
Opto-couplers are non-linear. This is true of the LED and of the photo-receptor - whether photo-diode or photo-transistor.
Figure 1. Close-up of the opto-isolator.
When an analog signal requires opto-...
- 176k
23
votes
Accepted
How does a 40 Gbit/s Ethernet interface process packets in silicon?
There are several ways how you can make a data link faster:
make more transmissions per second
send more bits per transmission
run several links in parallel
40G Ethernet does all of this: according ...
- 25.8k
17
votes
Is it possible to generate light with an antenna?
The wavelength of 750 THz is 400 nm so, your dipole would need to be 200 nm long to make a radiating antenna but your biggest problem (in 2021 and probably beyond) is being able to produce a frequency ...
- 457k
15
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How does a 4 pin RGB connector work without ground?
But there is a ground. Or actually, three grounds.
The three RGB wires are the grounds for the three LED colours.
The three colours just share a single +12V supply wire.
- 149k
12
votes
Accepted
Position of current limiting resistor
In your circuit, U23 is not a source of current into the Q25 base; it works by shunting base current away from the transistor. The base current is supplied solely by R110, so it's value should be ...
- 20.2k
12
votes
Can anyone identify this chip which I think to be an optocoupler?
I think it's from QT Optoelectronics, which was acquired by Fairchild in 2000 Fairchild was then swallowed up by ON in 2016.
The part does not appear in QT's 1995/6 databook, which is available ...
- 398k
12
votes
Is it possible to control the frequency of light?
Of course you can.
Tunable lasers are a thing; you can modulate different aspects of the light generation process in different types of lasers.
You can excite a laser diode with a sinusoidal signal, ...
- 94.9k
11
votes
How do I model an LED with SPICE?
First, I would point out that you can read additional diode parameters BV, Ibv and Cjo directly from the LED datasheet as "Reverse Current" Ir at Vr and as "Capacitance" C.
Adding to W5VO's great ...
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11
votes
Why is this circuit isolated?
That is not a very good illustrative diagram, and it's copied directly off the IL300 datasheet:
Here is how it should be connected:
The LED has an output that varies with temperature and decreases ...
- 398k
11
votes
Accepted
Can anyone identify this chip which I think to be an optocoupler?
Logo does not match, but perhaps a pin compatible version of Fairchild/ON MOC206 optocoupler with transistor output?
Fairchild datasheet
The logo resembles QP semiconductor, but I don’t find anything ...
- 14.7k
10
votes
Accepted
Typical wavelength range for solar cell measurement
Silicon's band gap is about 1.1 eV, corresponding (by chance) to about 1.1 um wavelength. Therefore a silicon solar cell will have practically no response to longer wavelengths than 1.1 um, and it ...
- 130k
10
votes
Is it possible to generate light with an antenna?
The other answers are correct, the frequency of light (i.e., visible light) is so fast that it's really hard to do. People do make THz light (even longer wavelength than infrared) using antennas, and ...
- 2,096
10
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How can we explain this strange phenomenon with an optocoupler switching?
The PS7122AL-2A-A is not just an optocoupler. It is defined as a SSR or Solid-State Relay.
On page 6, this datasheet states that \$t_{on}\$ is max 1.5ms and \$t_{off}\$ is max 0.2ms. 1/1.5ms = 667Hz,...
- 16.2k
9
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Why we use two photodiodes as optoisolator or optocoupler?
I think you might be referring to an analogue signal opto isolation technique like this: -
The op-amp on the left is driving an analogue signal across the optical barrier and, to make sure the ...
- 457k
8
votes
Is it possible to generate light with an antenna?
Here is an open access paper describing an Yagi-Uda antenna emitting light at 830 nm.
Kullock, R., Ochs, M., Grimm, P. et al. Electrically-driven Yagi-Uda antennas for light. Nat Commun 11, 115 (2020)....
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8
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Is it possible to control the frequency of light?
I mean, controlling directly in the source, not filtering the light or arranging density of the medium.
This is essentially what a tunable laser does. Internally a laser is an excited piece of ...
- 17k
7
votes
Q: Check if an LED in my circuit is still "good"
simulate this circuit – Schematic created using CircuitLab
Figure 1. (a) Monitoring forward voltage across LED. (b) Monitoring LED current by opto-isolator.
Figure 1a may provide the best ...
- 176k
7
votes
Increase LED Brightness
My guess would be that the Vce(sat) drops of both the ULN2803, the high-side transistor and the voltage drop on the current-limiting resistors could easily add up to roughly 2V or more, not leaving ...
- 1,719
7
votes
Accepted
Laser scanning: why are things like deflection and mirrors used instead of just a mount and servo?
A few thoughts:
Weight: moving a lightweight mirror will be easier than moving the laser assembly.
Speed: related to weight, the system response can be much faster.
Reliability: no flexing of wires ...
- 176k
6
votes
Should I reverse bias phototransistors?
Photodiodes are reverse biased to compress the space-charge region and reduce the junction capacitance. This allows higher bandwidth. There's no direct analogy to a phototransistor. Usually, ...
- 23.9k
6
votes
Accepted
How Gigabit Ethernet is achieved in fiber optics?
In the Gigabit Ethernet world, the media access controller (MAC) communicates with the physical layer chip (PHY) through the Gigabit Medium-Independent Interface (GMII)
The GMII is an 8-bit-wide ...
- 130k
6
votes
Trouble changing an optocoupler without changing circuit functionality.
Connect Vcc to pin 5 and connect pin 4 to the MOSFET gate. Leave pin 6 open.
- 173k
6
votes
Position of current limiting resistor
It makes no sense on either before or after the pull-up and can be removed.
- 149k
6
votes
Accepted
Why do we have a limited bandwidth in electronics?
I feel like there are almost two questions here
What limits the bandwidth of electronics? (Let's focus on solid-state electronics)
Why do optical waveguides provide such large bandwidth?
Side Note: ...
- 1,252
6
votes
Why do we have a limited bandwidth in electronics?
I've been looking around a bit on optical communications and it is said that the main advantage in using optical communications, namely optical fibers, lies in the gigantic bandwidth available, when ...
- 17k
6
votes
What is the purpose of using an analog optocoupler?
It allows an analog signal to be isolated between the input and output. A digital isolator can't do that for an analog signal.
- 149k
Only top scored, non community-wiki answers of a minimum length are eligible