Questions tagged [impedance-matching]

Impedance matching is a process of making one impedance equal to another another.

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Causes for negative port resistance of passive device (or obtaining |S11|>0 from measurements)

Suppose you have two reciprocal (passive) devices, A and B, both described with S-parameters \$S_a\$ and \$S_b\$. With a VNA, you measure \$S_a\$ and \$S_{\rm tot}\$ (S-parameters of AB, both devices ...
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Single trace width calculator for impedance matching

I would like to calculate the trace width of a dipole PCB antenna in order to match a 50ohm impedance. Obviously, there is no ground on the bottom side. All the impedance matching trace width ...
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3answers
428 views

Deriving the S-parameters, different Matched Loads possible?

I guess this is more of a conceptual question but for the problem below Im having trouble getting started on how to derive the S parameters for the network. I noticed that the network at 28.025 GHz ...
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50 views

Antenna matching using L-sections does not always yield a "matched" solution

I created a program to compute the component values of a T network to match a reactive load (R+jX) to a 50 ohm source, based on the procedure outlined by M. Walter Maxwell in his book "...
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64 views

Source Impedance Consideration for ADC

I recently used accelerometer ADXL335 in my academical project, this sensor gives analog output. I interfaced this sensor with microcontroller PIC18F458 using ADC module. It was successfully ...
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1answer
217 views

Unclear RF Schematic Reference for Power Amplifier Connection and Matching Network Properties

Background I'm trying to design a device with an STM32WL series MCU using the UFBGA-73 package. There is only one reference circuit given for the RF portion of the MCU in an application note (pg. 6) ...
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72 views

Impedance matching on oscillator

I have built an oscillator configuration at 4-7GHz. At 5.29GHz, the output of the oscillator has resistance R=-189-j*51. How can I use impedance matching and a bandpass filter since I have a negative ...
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5answers
113 views

Why is output power such a meaningful quantity in speakers?

Loudspeakers, for example, should be impedance matched to deliver the highest power from the source to the speakers. But why do we care about power so much? A speaker is at its simplest, a coil around ...
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1answer
108 views

How to send this signal to a mixer?

I have the receiver which works when I wire a Hifi on the output. But when I try to send the signal to the port 2/3 of the following mixer then I don't have any signal anymore. I guess I need to ...
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3answers
244 views

Impedance matching resistors for digital output

My circuit has to emit an S/PDIF digital audio stream over an RCA connector. According to the specs (from Wikipedia) the signal should have an output impedance of 75Ω and a peak-peak voltage of 0.5V. ...
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1answer
65 views

Not matching 50 ohm impedance

For my RF circuit (868MHz), I need 50-ohm impedance. When I calculate the impedance as PCB manufacturer layer stack-up, the impedance would be 66 ohms. How does this affect my RF circuit performance? ...
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1answer
79 views

Resistors in high-speed I/O trace when impendance mismatching

I am little bit confused over impedance matching when dealing with high-speed digital I/Os. I would like to share some perspectives in hope to clarify a few things. Let's consider a digital output ...
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53 views

How to deal with simulation/measurement discrepancies of simple RF circuits (e.g. matching) without access to expensive equipment?

Designing a circuit (PCB) operating at low frequencies is fairly straight forward. However, my design includes a simple RF frontend. The frontend consists of usual componenents on a PCB (SMA connector,...
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1answer
46 views

Matching line driver output impedance over wideband

I'm designing a high impedance line tap for 10-10GBASE-T ethernet signaling. In the AFE I have a JFET LNA for high input Z which goes to a var. gain amplifier that is a fully differential ADC driver. ...
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1answer
96 views

RF Matching Net

I am projecting a system that contains two RF chips, a LoRa SX1276 (915MHz) chip and a ESP32-D0WDQ6 (2.5GHz). In the schematic bellow, the ESP32 (2.4GHz) design has a matching net between the chip ...
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314 views

How do you match an LDMOS FET to 50 Ohms?

I'm considering using one of the following LDMOS FETs as an RF amplifier: AFM907N (8W) AFT05MS031NR1 (30W) AFT05MP075NR1 (70W) The datasheets provide \$Z_{source}\$ and \$Z_{load}\$ metrics for some ...
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143 views

RF Matching Problem

I am having some fundamental issues trying to create an impedance matching network for an 868MHz antenna, I have a PI network between the antenna's connector and the antenna feed point I have measured ...
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1answer
73 views

Controlled impedance traces necessary between line driver and series termination resistor?

I'm designing a line driver circuit with the SN74BCT25244 chip. The chip has a rise time of ~10 ns into an open circuit based on my own scope testing, but we are only wanting to drive the signal at a ...
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166 views

CAN Bus Nominal Impedance

I understand the reason for choosing a termination resistor of 120 Ohms for the CAN bus to avoid reflections but why was the nominal impedance of the CAN bus cables required to be 120 Ohms by the ISO ...
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1answer
96 views

Op amps with load impedance matching

I have a THS3491 Op amp, and want to use non-inverting configuration. Reading through the datasheet, all the specs are defined with \$R_L=100\Omega\$. So, does this mean I have to attache \$ 49.9\...
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76 views

Can I debug this simple circuit without VNA and proper RF equipment?

I am debugging a very simple circuit (existing PCB, not designed by me) that downconverts an AM modulated signal at 900 MHz: The problem: What I measure at "Vo" does not match my LTspice ...
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263 views

Does matching impedance connectors matter in non-RF signals? Why?

I am designing a PCB which communicates with an encoder over RS422 at 2Mbps (15ns rise time typical in the MAX490's datasheet), and I am currently selecting the connectors. I have found 120Ohm twisted ...
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1k views

How does load resistance affect RC low pass filter?

I am building a low pass filter. This is the equation I'm using to calculate what frequencies I want to pass though, but I have a couple questions on details. $$ f_c = \frac{1}{2\pi RC} $$ What goes ...
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1answer
82 views

What is the difference between a Line Impedance and Charecteristic Impedence?

I am thinking this from long time. In case of Digital Circuits, I know that, whenever a signal is incident on a PCB trace, for example, there may be an AND gate, which just switched output to 1. Then,...
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231 views

Does it looks like a bandpass matching network?

I am trying to understand this receiver and figure out what does this L-C network is. I read about matching networks and found this example, I am curious if it is the same thing. is it? In the ...
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32 views

Flipped length and Z-matched lines. How to pcb patch?

I think the title says it all. I accidentally flipped the P and N lines downstream of a CSI/MIPI retimer (they are impedance and length matched). Is there any way at all to patch this on the pcb?
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401 views

How voltage and power transfer in cascaded amplifiers work?

When there are three amplifiers that are cascaded to produce higher gain: The source resistance should be lower than input impedance of first amplifier The output impedance of first amplifier should ...
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1answer
92 views

Coax Cable Wave Impedance, Capacitive Load

I am studying the behaviour of cables over frequency, especially what a source sees, and have 2 Questions, as I did some simulations in LtSpice. As a model for the cable I used the "Lossy ...
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1answer
43 views

Parallel trace signal integrity: Increasing width to match characteristic impedance vs increasing trace gap

Imagine you are routing a large number of single ended high speed traces through a long narrow gap on a PCB. Lets say these are ultra-high speed SD signals, so a 208MHz clock. The traces should be ...
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2answers
209 views

How to connect a low impedance RF amplifier to an antenna?

I'm trying to maximize power transfer from my amplifier to my custom antenna, but am unsure about how to properly impedance match the system. My amplifier has an output impedance of 4Ω, but is ...
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5answers
3k views

Coax cable - capacitive load

I still have an understanding problem with impedance matched coaxial cable and its behaviour. We do impedance matching to prevent reflections. How does my signal source see the whole cable? At a ...
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1answer
39 views

Load to Source impedance match for non-constant load impedance

i have a rf-system that is working in frequency range of 100 MHz and try to match the impedance of the load to the source system (50 Ohm). So, in general, i know that a network (P- or T-Network) has ...
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222 views

Impedance Matching between Source and Load

I am having this basic doubt In the basic crude basic block diagram, we have a source, transmission line and load, all having an impedance of 50Ohms. But according to maximum power transfer theorem, ...
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1answer
86 views

Impedance Matching of an Antenna

I am reading about antenna design and have a few questions which I could not get clarified. I read about "Stubs". I got to know that Stubs are used for impedance matching of an Antenna either by ...
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1answer
96 views

Voltage Follower Circuit Output Changes based on Load Resistance

I am trying to simulate a circuit which can act as a voltage follower for a headlight. I simulated the circuit using CircuitLab. I simulated two conditions: When headlight resistance is 10 Ohm. ...
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4answers
2k views

Why should a receiving antenna be impedance matched to 50 ohm instead of a lower impedance?

I'm in the process of getting to grips with RF design and am having some trouble understanding why we should always match antennas to \$50\Omega\$. I understand from the maximum power transfer ...
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65 views

Why is an attenuator placed on the scope end and not the PCB end?

I've noticed when adding an external attenuator between PCB and the scope (1MOhm) that it is placed in this manner: PCB -> SMA Socket -> SMA Cable Plug -> SMA Attenuator -> SMA-to-BNC -> Scope Why ...
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2answers
53 views

How does Impedance matching equation work out from original link?

From this link: L-Pad Impedance Matching Equation How do you get those two equations? They do not look like a voltage divider formula, do they? Questions repeated here: First answer from Adil ...
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30 views

Antenna impedance matching within metallic enclosures

What im trying to achieve is kind of an chip antenna breakout board, since it must sit within a metallic groove. The plan is a PCB of 10mm diameter with an U.Fl connector on the back and an antenna ...
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53 views

Should I cut away the ground pour above a diffpair on the first inner layer, which are Z-matched to the ground layer (L2)?

I'm routing diffpairs on the 1st inner layer of a 4-layer pcb which are Z-matched to the 2nd inner layer which is entirely a ground pour. The top layer has traces and routing AND also a ground pour ...
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1answer
279 views

PCB Antenna Tuning

I am trying to tune an antenna as seen above, using this wonderful Smith Chart Tool. It needs to match 35 + 10j characteristic impedance. I have found a tool like the Microstrip Impedance Calculator ...
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2answers
99 views

Speaker impedance and voltage

There is a device which has output impedance 150ohms. If my headphone has either lower(30ohms) or higher (400ohms) impedance can I use it or sound will be too low/high and it will be unsable? Also, ...
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Determining Z1 for voltage divider of RF Matching Circuit

I have a problem where I was given an RF circuit with a series RL load. I am tasked in finding a matching L circuit and determining the values of the components. I used a smith chart to determine that ...
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1answer
109 views

How to calculate component value of a matching network

You can already expect my knowledge level In antenna designing (newbie). This may be or may not be a stupid question. The reason is I don't know about this very much. Iam designing a PCB for ESP32 ...
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1answer
87 views

Can 3Ω speakers match 4~16Ω amplifier? [closed]

I have a set of Samsung home theatre system. The Samsung DVD player is no longer working. I would like to get a new amplifier and reuse the 5 existing Samsung speakers. But the existing speakers are ...
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1answer
66 views

Understanding series open stub tuning

I recently had an assignment where I had to use open stub series tuning to find a way to maximize power delivered to the load from the generator. I understand that power delivered to the load is ...
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1answer
63 views

Padding/impedance matching of a phono input

My old stereo amp got coffee spilled on it. I replaced it with the latest model from the same manufacturer. I am an old-world person, and prefer simple approaches - i.e., radio buttons to select ...
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59 views

Best way to connect a coil to a source with 50Ohm impedance?

I have a 50Ohm impedance source at 800Mhz and a coil with complex impedance Z = 0.0028 + j3973.9121 Ohms at 800Mhz. I would like to maximize the current through the coil and protect the source. I ...
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1answer
63 views

Which Signals require impedance matching?

There are two types of connections in PCB. Which are in between the PCB.(e.g- A SD card is connected near to Controller) One is going out through some connectors.(Some UART or SPI going out through ...
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32 views

32F746GDISCO Stackup and Ethernet Impedance

I have an example board with PCB about the ethernet application. I noticed a mismatch between stack up and ethernet lines, or something else I don't know. Ethernet Lines are drawn with 0.125mm and its ...

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