13

Even if ambient temperature is well controlled, air currents can cause noise if there is significant voltage across the capacitor. Capacitance degradation with time is different for different dielectrics. And the big one, voltage coefficient of capacitance. If you can use them, NP0 caps suffer from such effects much less than X5R X7R etc. parts, but they ...


13

Thanks for everyone's help. I believe Bruce Abbott has given the correct answer. I'm posting from my bed and I cannot test it yet until tomorrow, but The analysis below is confirmed, when he mentioned the word "refresh", I think the problem is already solved. I knew how Z80 refreshes the memory, but completely forgot about it in the previous days. ......


12

The point of this probe is that the scope has its 50Ω termination enabled. Since the scope input impedance is matched to the cable, there is no reflection from the scope. Once the load side is matched, we don't need to worry about any source-side impedance mismatch; reflections have already been suppressed. The point of the 950Ω resistor on the input side ...


8

Ensure that you have adequate decoupling capacitors on all your ICs. A 100nF ceramic from power to ground on each IC keeping its leads as short as possible and a low ESR electrolytic say 100uF on the breadboard across the power rails.


7

The spikes at the rise and fall of the blue signal are probably due to probe inductance (aka long GND wire connection). Try using as short as possible GND connection. Also as much as possible, for scope measurement get rid of the hookup wires and use the probe as close as possible to the final destination of the signal. For example if the Pi is the SPI ...


6

This is more a completing note than a full answer, since Spehro Pefhany and crasic have already detailed the main characteristics of main types of ceramics capacitors. However, they left out a topic which was known in the circle of Audio Electronics Engineers up to few years ago: ceramics are dispersive dielectrics (as practically all existing dielectrics ...


6

Market reality will often dictate your choices it becomes exceedingly difficult to find class 1 dielectric parts in common packages with high voltage (>10V) or high capacity applications (>1uF) , you will likely not be able to simply "spec" a better dielectric and expect that your BOM is realizable. The market has decided, generally, that NP0 and other ...


6

IMHO the integrity of the shielding is what matters. Without shields, RFI and EMI and black-brick switching-requlator spikes are aggressors into and onto the audio. Foil may be best, but foil is fragile. Thus multi-layer woven copper-braid [many small wires in the braid, dense enough to block the passage of light] shields should be your goal. Been working ...


6

Short answer: You are absolutely right not to worry about the smaller pullup resistors, since your bus will be in a high state the vast majority of the time. Moreover, the slow rise times will probably increase the power consumption significantly. Just use the 2.4kΩ resistors. Long Answer Very slow edge rates will actually cause CMOS inputs to consume ...


4

I see two possibilities here: 1) D0 is tristated Whatever was driving D0 goes to tristate (high-impedance mode) and then a pull-down somewhere in the D0 net brings the voltage down slowly (time constant defined by the pull-down resistance and the parasitic capacitances of ICs and traces). The exponential nature of the waveform is a strong indication that ...


4

Looks fine to me. You could split it in two at the middle and go both ways (don't join them at the far end) but I don't think it's very important for only 80mm total length. Make sure you have pullup resistors commensurate with your capacitive loading and drive capability of the weakest chip.


4

The resistor will indeed reflect the incoming signals back, but those signals exist in a few mm of IC pin + resistor pin, which have an infinitesimally small inductance. Thus those reflections will not be enough to produce any measurable overshoot. On the other side of the resistor, a source with ~1kOhm resistance feeding a 50 Ohm cable will create a ...


3

Can I transmit an analog signal through a noisy environment without it being corrupted, or should I use a digital signal instead? Yes, you can transmit analog signals long distance without them being corrupted, but proper EMI technique needs to be followed. The usual route is to gain the signal up at the sensor and then use shielding on the cable from the ...


3

This is not something that can be solved with filters alone. Your SNR is negative at 60 Hz and for everything above 108 Hz, and it's only at most +0.1 dB below that. The only way to extract the signal in that case is to have a lot of a priori knowledge about the signal itself that allows you to distinguish it from the noise. For example, if you know that ...


3

I didn't read your entire wall of text, but I don't think the answers to your questions depend on much of what you wrote. I have the datasheets of both ICs. Where is it written, implied or can be calculated/extracted the input/output impedance of the pins? Different vendors have different conventions for how they report it. One might report an output ...


3

You have three things to worry about: heat, voltage drop, and interference. Interference between your DC and RF wires is probably the least of your problems, unless your high-current lines dump noise onto the RF lines, or the RF lines are really powerful, and dump enough energy into the DC lines to cause problems for whatever you're powering. For the heat ...


2

At 1MHz you have nothing to worry about. I've committed atrocities such as passing 8MHz SPI over 30cm ribbon cables with impunity (maybe I got lucky!) When you go higher, say, 30MHz, you have to start worrying about controlled-impedance traces, matching lengths, not taking sharp turns or having vias, and so on, but you are nowhere near that operating regime....


2

Do this on the inputs. The variable resistor is the remote thermistor. How concerned are you, about voltage drop across the 10,000 ohm resistors? Notice we use the 1uF to heavily filter the trash injected. The assumption is that the injected electric-fields and magnetic-fields have ZERO average current, and thus heavy filtering ---- by a capacitor or in ...


2

Communication Theory tells us the optimum SNR is when the signal BW is maximized and Noise BW is minimized with a "Matched Filter" This means the filter passes with the matching spectrum and while blocking the spectrum of noise with the same shape filters as each spectrum with some consideration to phase requirements. Here is a situation where the noise is ...


2

However, the outer transmission line is longer than the inner transmission line because of the bend, thus, V- travels a longer distance than V+, so should I see a the two signals appears on the oscilloscope in different time with V+ arrives at oscilloscope earlier? Yes, this can happen. It also causes differential-to-common-mode conversion which can be bad ...


2

At 16 MHZ ordinary ribbon cable should be fine, I'd look at using PATA (hard drive) cables, because they are available off the shelf cheaply. I'd interleave the 16Mbaud data, with power and ground wires G d P d G d P d G To reduce cross-talk and also separate the clock from that by a little bit all the other signals as slow enough that they should not ...


2

There are two potential issues that come to mind: Signal integrity affecting reliability of communication. Although you don't say so explicitly, I'm assuming you don't see any indication of corrupted data in either direction. But that's not enough - you want to know how much margin you have, both in time and in voltage, to datasheet guaranteed thresholds. ...


2

At 50MHz, the wavelength in the PCB is about 20ns x 15cm/ns = 300cm. The time of travel in a wire of 30cm is 2ns. If you want to avoid to consider you traces as transmission lines, you must keep them under 1/20th of the wavelength, which is 15cm. And at that length you need to account for the 1ns signal delay when checking hold and checkup times. You ...


2

Yes, it is possible to make a wideband power splitter with matched input and output impedances, but the signal level is reduced by half, which greatly limits the length of cable that you'll be able to drive. Also, the physical layout is very critical for flat frequency response. There's more information here, but the basic idea is this: simulate this ...


2

Justme's answer is sufficient: There's pins that logically can't be split passively. And no, they are not optional; especially working E-DDC is a mandatory requirement for HDMI. Other than that: The signal lines aren't just "cables", they carry a very high-speed signal over impedance-controlled lines (typically, twisted pairs). If you built a splitter, ...


1

For a diff pair, having a mismatch not only reduces the data eye pattern margin, but it also causes common-mode current for the uncancelled portion of the signal. This will show up as noise on the ground reference alongside the pair and can be a big EMI headache. This is a huge problem for example with HDMI on the driver side: unequal trace length adding ...


1

The inverted signal will be phase shifted compared to the non-inverted. If the imbalance is a significant portion of the wavelength, there will be noise issues. Noise is emitted because the EM fields of the signals don't cancel each other like they do on a matched pair.


1

The measure of low frequency (< 100MHz) shielding effectiveness is called transfer impedance. The coaxial cable was invented by Heaviside over 100 years ago. ANSI/NEMA WC 61 January 1, 2005 This standard is intended to provide a reliable surface transfer impedance (STI) test method for coaxial cables and shielded multiconductor cables over the ...


1

You asked if shielding affects signal integrity: Yes, of course it does. Shielding changes the characteristic impedance of the transmission line model. Concerning your ungrounded shield: It might reduce external magnetic field coupling (inductive coupling) a little, but it does certainly not reduce magnetic field coupling between the cable signal lines. ...


1

This is a point to point link? Then source termination by the drivers output impedance is probably all you need if you can configure the driver to match the line impedance (which it sounds like you can). If for example, the driver is 50 ohms and the line impedance is 50 ohms driving a cmos input (so essentially a slightly capacitive open circuit) then ...


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