Questions tagged [controlled-impedance]

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2
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1answer
54 views

PCB Thickness Variability

How much variability is there in the thickness of a standard PCB? Let's say I order a 1.6mm FR-4 board. Will the actual thickness range 1.5mm-1.7mm? 1.4mm-1.8mm? 1.59mm-1.61mm? What is the (...
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0answers
25 views

Lumped vs Distributed System when connecting to Cables

I am currently working on a project where I have a microcontroller that is talking to a SPI to UART IC and then that IC is talking to a UART to RS-485 IC. This is then connected to a 120 ohm ...
0
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1answer
94 views

Altium - design rule check does not match with signal integrity for impedance

I have designed a 2-layer PCB with Altium Designer. I placed an impedance rule of 50 Ohm in trace width rule section. When I run the design rule check, there is no impedance error. However, when I ...
0
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1answer
86 views

When is it important to handle reflections in pcb design?

I am watching some videos explaining how reflection can affect a signal and how you should treat these signals as transmission lines to remove reflection. I wanted to understand a more practical ...
1
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1answer
79 views

PCB controlled impedance

Hi) I want to calculate the width of my 100Mb Fast Ethernet MDI diff pairs. I've got some software (TXLINE 2003 Microstrip). I have 4 layers. The second layer is GND, the third is power, top and ...
2
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2answers
449 views

Controlled Traces Length in SD card

I my new design I need to use SD card communication. I would like to match all the impedance traces and control the length of the traces. Regarding the controlled length, is there a rule of thumb to ...
2
votes
1answer
803 views

Implementing 1000BASE-T (Twisted pair) over PCB backplane [duplicate]

Problem: We are designing a small payload which will contain several ethernet capable devices connected via a backplane we must design. All guidelines concern the scenario where the PHY is ...
0
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2answers
65 views

Transformer getting hot

I have build an LED array consisting of 75leds, 5 connected in series with a 39ohm-1/4watt resistor and 15 such series connected in parallel to the rectifier circuit having 2-IN5408 diodes and 1- ...
1
vote
1answer
1k views

What should the single-ended impedance be for LVDS?

For LVDS, it seems like the traces are usually specified as 100 ohm differential impedance. What should the single end impedance be from each trace to ground? I'm looking at PCB impedance ...
1
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2answers
2k views

Designing a 50Ω coplanar waveguide on 1.6mm FR4

I'm trying to design a 50Ω coplanar waveguide to connect the output of a LoRa module to a SMD metal antenna. The two images below show the top layer (red) and bottom layer (blue). Vias are green and ...
1
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2answers
41 views

While performing the controlled impedance routing what about the current flowing through it?

While calculating the conductor impedance the parameters that we consider are the conductor width, conductor thickness, frequency & substrate parameters. For achieving the particular impedance ...
15
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5answers
2k views

Why doesn't controlled impedance depend on track length? [duplicate]

High speed design noob here. Resistance increases as wire gets longer, but I found in saturn pcb calculator the impedance depends only on track geometry and distance from plane. Say for DDR3 single ...
1
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2answers
157 views

BGA break out and impedance control

I'm connecting two BGAs (0.8mm pitch) which are DDR3 signals. Vendor recommends 40 and 80 ohm for SE and diff traces. My PCB manufacturer suggests the following specifications for the diff traces: <...
0
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1answer
554 views

Digital pot (MCP41100) as LED strip dimmer

I want to be able to dim a led strip with a MCP41100 but I have no idea how to connect the digipot to the led strip... It is connected to an ESP8266. I will have to figure out how to address the ...
0
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1answer
474 views

Reflections on a differential transmission line

I understand why reflections occur when there is an impedance mismatch on a single-wire transmission line. However, when we introduce a differential line, I am having trouble picturing what would ...
2
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2answers
617 views

PCB Trace Impedance - Multiple Layers

I'm in the process of designing an 8 layer PCB with a stackup of: Signal, GND plane, Signal, Power plane, Power plane, Signal, GND plane, Signal. For calculating the trace widths necessary for ...
1
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3answers
414 views

New led lights flickering in shop

I have replaced several light fixtures with LED in my company. The 400 watt hi-bays I replaced with 95 watt LED. They work great. I replaced a set of office lights that were track halogen with 7 watt ...
4
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1answer
2k views

Is this layout good? (RF - 2.45 GHz)

I finished laying out HACK, my first RF (2.45 GHz) layout. The sensitive part is the connection between the IC (Atmel SAM R21G18A), the balun (Johanson 2450BM15A0015), and the PCB antenna (copied from ...
7
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2answers
777 views

Testing of impedance test coupons

I have a board with a 50 Ω impedance controlled track. I have got the boards manufactured. The manufacturer has sent me 2 additional boards viz - test coupons. I understand that test coupons have the ...
4
votes
1answer
1k views

What are “slash sheets”, and how do they relate to PCB substrates?

I am trying to specify the stackup for a PCB. Previously I have used whatever the board house considered to be their "standard" stackup. This time I am looking at using FR-408 (pdf) because of its (...
8
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2answers
10k views

Length Matching Differential Pairs

I am routing a PCB with an Ethernet connection and I am having a bit of trouble deciding on how best to route the TX and RX differential pairs. I have done the impedance calculations to figure out the ...
3
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3answers
268 views

Controlled Impedance Microstrip Frequency

Are you supposed to calculate the characteristic impedance for the frequency you are using or at 1GHz? I see pretty much everything calculated at 1GHz in all examples and papers. For example - for ...
0
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1answer
429 views

SMD LED Perimeter Lighting with PWM for Dimming on each colour

simulate this circuit – Schematic created using CircuitLab So from the start what Im trying to achieve is drive way lighting in which each colour is separately dimmable with a pulse width ...
1
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2answers
1k views

Automatic impedance matching in microwave waveguides

I am trying to building a magnetron plasma using microwave magnetron. I now need to build magnetron to antenna link using rectangular waveguide, WR-340. I then found out that it needs to be tuned ...
1
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2answers
3k views

Internal USB (FFC?) cable with 90 Ohm Differential impedance

I'm trying to run USB D+/D- signals and some unrelated 19V power between two PCBs, on the daughter PCB the USB D+/D- will terminate to a USB-A-F jack. I have no problem maintaining 90 ohm differential ...
8
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2answers
14k views

Why Characteristic Impedance must be 50 ohms?

Where does this number come from? For single ended it must be 50 ohm and for differential pairs 100 ohm. Why? For PCB with controlled-impedance these are that common numbers. Outside of the PCB you ...
5
votes
2answers
314 views

Can I slow a CMOS output through an RC filter?

Is it good practice to slow down the slew rate of a CMOS output by putting an RC filter on it? What happens with impedance matching after I do this? Or can I just set the RC filter with such a low cut-...
16
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1answer
2k views

Reasoning behind Ethernet pair order

An Ethernet connector seems to use a surprising choice of signal placement in its RJ45 connector. Does anyone know the reasoning behind: The decision to make pair 2 straddle pair 1? Why Ethernet uses ...
2
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1answer
863 views

Signal reflections at the driver?

This question is related to How do I use directional couplers on a differential signal? I understand that if I have an impedance mismatch at the end of a signal cable, E.G. from a terminator which ...
7
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3answers
4k views

DDR1 Layout Considerations - DOs and DONTs

I am novice to high speed design. Before getting in to DDR, I recently learned about impedance matching and how it is done, likewise I learned about length matching and how it is done.(Baby steps ...
6
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3answers
1k views

Controlled impedance in presence of vias and through-hole components (PTHs)

We have some controlled impedance traces on layer 4 of a board. Layer 3 is a GND plane. Layer 5 is a 3.3V plane. Both planes are unbroken (they occupy the entire layer), with the exception of vias and ...
2
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2answers
6k views

When does controlled impedance on a PCB matter?

Suppose I have a PCB that contains a microprocessor, or an FPGA (a "controller"). This "controller" drives a single-ended signal to an LVDS driver IC and a single-ended signal to a connector that goes ...