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Questions tagged [impedance-matching]

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

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873 views

Find impedance matching in a quarter wave transformer

I would like to know if there is a way you can find the impedance that has to be set between the load $Z_L$ when it is complex and the characteristic impedance $Z_0$ to have impedance matching ...
235 views

CAN-Bus: Wire Impedance vs Terminal Resistor

I'm seeing several pre-fabricated "CAN-Bus" cables with (2) DB9, 120 ohm terminal resistor connections, while the cable's impedance is 100 ohms. A. What is the purpose for this mismatch? B. ...
286 views

Does a power amplifier dissipate power in its source impedance?

If I have a power amplifier (or other signal generating device) that has a source impedance of 50 Ohms and drives 1W into a 50 Ohm load, does it also dissipate 1W in its source impedance? My current ...
1k views

Quality factor in antenna matching / question about SX1261 LoRa transceiver

I have a question about how the quality factor is determined for RF antenna matching, especially for PI network matching. The reason for the question is the Reference Design for antenna matching for ...
268 views

PCB design for high-frequency differential lanes (PCIe and USB)

I have designed an M2 adapter which converts from KeyE to KeyM. Practically this means my board can be inserted into a KeyE slot, and it can host a KeyM SSD. Gray rectangle is the KeyM socket on my ...
67 views

Impedance matching before or after connector

Suppose I have a device which needs to have its impedance matched to some incoming generator at one specific frequency. This device is placed on a PCB and a trace is connecting it to a 50 Ohm SMA ...
89 views

Power analysis of transmitting antenna equivalent circuit

I'm currently taking a course about antennas, based on the book "Antenna Theory: Analysis and Design" by Constantine A. Balanis. The Thevenin equivalent circuit for a transmitting antenna is ...
1 vote
1k views

Impedance matching for ESP32-D0WD-V3 QFN 5x5 connected to uFL port

I'm designing a PCB that uses a ESP32-D0WD-V3 QFN 5x5 and I want to have a uFL port for 2.4Ghz Wifi/BLE. Directly from the datasheet, I get the following note: The output impedance of the RF pins of ...
79 views

Using a series of attenuators for a sampling HF transmission math or design errors/misunderstand/ignorance

TLDR: Why does my math not work. SITUATION: I have a 1.5KW 50 ohm RF dummy load for ham radio and I'm trying to design a sample port for monitoring with a spectrum analyzer. I have now realized that ...
1 vote
552 views

Troubleshooting noisy FET buffer for contact mic

I'm trying to follow the schematic on this page to create a preamp/impedance matcher for a balanced piezo contact mic. I've reproduced the schematic below. I've built it on a breadboard and I'm ...
70 views

Impedance considerations

I'm desiging a PCB which uses USB (2.0) and PCIe (2.1). USB is not that fast, however it's said its impedance might have to be correctly set to around 90Ohm +/- 15%. Now on the other hand, PCIe's ...
45 views

LVDS to Singled-Ended - Transmission Line Balun Matching

I need to convert a LVDS clock into a single-ended signal. In the past I've used a voltage balun with a center tap on the secondary but I haven't found any good past 1GHz. I need to get to 2GHz in ...
191 views

Why does "impedance matching" in the context of reflections demand that resistive impedance and reactive impedance are treated separately?

I have assumed that for reflections, Ohm had to be matched between source and load, but resistive and reactive impedance did not have to be matched separately. I was told this is wrong, and that ...
152 views

Impedance matching in RF and complex conjugate (Maximum power transfer theorem)

The "maximum power transfer theorem" states that "maximum power transfer occurs when the load impedance is equal to the complex conjugate of the source impedance", that "for ...
197 views

Can reactive components affect resistive impedance of circuit (Smith chart question)

I'm failing to understand something. Impedance matching by complex conjugate can be defined as this: "For two impedances to be complex conjugates, their resistances must be equal, and their ...
1 vote
74 views

Matching a 50 Ω amplifier output to a 50 Ω SMA connector on a PCB

Silly question: Say I have an amplifier with a 50$\Omega$ output and I want to connect it to an SMA connector. As far as I understand I need to match the 50 ohms to maximize the power transmitted. ...
230 views

Choosing RC values for Active LPF to match signal input impedance

I am design a basic 1st order Active LPF with unity gain and am new to this field. How do I make sure that I choose my R and C values to match the input signal impedance or does this not matter? What ...
911 views

Modern piezo microphone impedance-matching circuit

I want to record sound with a piezo transducer. I am connecting it to my sound card's input which has a good mic pre-amp. The levels are quite good and the sound seems quite clear but there's a lack ...
1 vote
1k views

Quality factor and frequency bandwidth in a matching network

It is known that the quality factor appears in the formulas for transformation of an impedance series bipole to a parallel one. A simple example is this one: Now I have three questions: I have ...
89 views

Impedance matching a function generator and a laser source

I am using a function generator to generate a sine input to a modulated laser. The function generator has output settings of 50 Ω and High-Z, while the laser for some reason has a 1 kΩ input impedance....
248 views

Difference in the characteristic impedance of a low frequency signal

In one of my PCB design, for a RS 485 signal termination resistor of 120 ohm is there. But the differential characteristics impedance of the signal is taken as 100 ohm instead of 120 and the signal ...
340 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 ...
212 views

How should I route the ground plane under a RF trace with a LC balun?

I'm designing a PCB with a ESP32-PICO-V3, with a RF output to a 50 Ohms U.FL (Micro-Coax) connector. The chip supports WiFi and Bluetooth in the frequency range 2.45 +/- 0.45 GHz. Right now, I have a ...
3k 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 ...
1 vote
340 views

Antenna pi-network matching High or low pass?

I am a beginner in RF system design and I have some questions. I have a PCB trace antenna, I need to tune it to 2.45GHz, this is for Bluetooth low energy communication. I want to use a pi-network for ...
1 vote
32 views

Resources for impedance matching networks

I am working on my first hobby PCB design project that includes RF components. On one hand, I have a 2.5GHz WiFi signal and an 868Mhz LoRa signal. I copied the matching networks from the reference ...
639 views

ADS Simulation: Schematic to find input impedance

I'm following a paper, using ADS, to find the input impedance of a shunt Schottky diode. The paper's schematic is Fig. 1, and my schematic is Fig. 2. I could not get the same result as the paper ...
314 views

Why is the balun transformer shorted and not simply removed?

I use a normal balun to match my 300 ohm antenna to my 75 ohm tuner (for "over-the-air" digital TV): I opened this balun up and found the typical circuit: Since the second coil from the ...
786 views

Matching impedance network for an LC ladder network

Let's say I have a 5 stage L-C ladder network with L= 4.7 micro Henry and C= 60 pF. The characteristic impedance of the network becomes 280 ohms (square root(L/C)). However, from circuit analysis, the ...
40 views

Weired result of Ltspice Zin measurement, Phase shift of -104°

I am trying to measure the input impedance of this amplifier to design a matching network for it. But the input impedance I get has a phase of -104° at the frequency of interest. I thought that Phase ...
549 views

Cannot trigger digital logic because half of source voltage is lost in impedance matching

I am using a 3.3V output of an NI controller over a coax transmission line. I have matched the termination resistor to the 50 Ohm source resistance. I need to use this output signal to control three ...
1 vote
770 views

Impedance matching a capacitive source

I am trying to work out how to match a current source coupled with a capacitor to a 50 Ω load for maximum power transfer. Specifically, I have a 6 pF PIN photodiode which driven by a 2.5 GHz optical ...
1 vote
95 views

Impedance matching 133 MHz - Topology and terminating resistor concerns

I am using the QSPI bus of the RP2040 to talk to a flash chip. I am also putting 8 more chips (PSRAMs) on that bus in my design, and a second RP2040 to load them. The datasheet for the RP2040 isn't ...
1 vote
41 views

PCB Newbie Stackup understand questions

I want to design a board with 6 layers up to 1.8mm thickness,120ohm diff and 90ohm diff ,SE 50 ohm and the manufacturer sent me this stackup: 12 mil for SE-50ohm not too thick? what is the material ...
36 views

HDMI: What is the maximum acceptable differential impedance variation and for which length

Imagine I have a HDMI bus with differential impedance 100 Ohm and length 10cm Imagine that for a segment of length "L" there is an impedance variation of "DELTA" Question: in order ...
64 views

Via for 50 Ohm impedence track to U.FL connector

There's a 4G LTE modem along with GNSS capability mounted on the bottom layer of a 4 layer PCB. Its a 4 layer PCB with JLC04161H-7628 Stackup. 50 Ohm impedance trace needs to go to U.FL connectors on ...
30 views

Why does the normalized input admittance have to be 1 +j0 to achieve matched condition at MM'?

In section 2.11.1 in the book Fundamentals of Applied Electromagnets by Fawwaz T. Ulaby, it says that in order for the circuit below to be matched at MM', y-in must be y-in = 1+ j0. Why is this so? ...
37 views

nRF52832 impedance matching values alternate solution

My question is all about to confirm or correct my understanding of impedance matching ckt. During fabrication we take care of transmission line of 50 Ω. Currently we have reference values as shown in ...
1 vote
58 views

USB audio (TRRS) to transformer for impedance matching

I'm kind of stuck, and not really sure where to look, or what to look up. I need to take the output of a USB audio fongle that has a single 3.5mm jack (TRRS), into a break out cable, and then need to ...
4k views

Impedance Matching Resistors on MII Ethernet Lines

Microchip is taking forever to activate my account so I will ask this here... I am using the KSZ8081 PHY for MII Ethernet. https://www.mouser.com/ProductDetail/Microchip-Technology-Micrel/...
50 views

How to match a network over multiple frequencies?

I'm trying to match the following network using the Matching Network Designer so that the resistance curves (solid lines) get pulled towards the horizontal line and the reactance curves (dotted lines)...
1k views

Qucs model for 2.4 GHz matching circuit

I am designing a matching circuit for an EFR32BG13 SoC. The current board layout looks like this: In addition to the visible layers (top and bottom), layer 2 is a solid ground plane and layer 3 is a ...
59 views

Why do LDMOS RF power transistors have a low real resistance?

I've been looking through datasheets for RF LDMOS amplifiers for use in an RF power amplifier. They typically have an input impedance that has some small real part of the resistance (<10 Ω) with a ...
260 views

Calculating lengths of single-stub transmission line when all 3 characteristic impedances differ

Consider a transmission line circuit like the following but where $Z_{o2}$ was also unique (say $Z_{o2}=7\,\Omega$): I know how I would find $l_1$ and $l_2$ using smith charts: Re\left\{Y_n(...
342 views

Antenna Coupling via Capacitor 4: Calculation of Q of 'by hand'

Consider following coupling of antenna to a LC-tank via coupling capacitor C1 and on the right the replacement circuit of the antenna: I have become aware of a serious knowledge gap of mine with ...
448 views

Question on matched 3dB attenuator

For the second picture below, how to derive the expression for Vo? I suppose there is some inbetween maths that I missed. Note: 41.44 Ω is the parallel equivalent for (50 Ω + 8.56 Ω) || 141.8 Ω.
1 vote
50 views

Matching network for a resistive matched source, line and load?

Suppose we have a well designed 50ohm antenna and source (as there are in many RFIC, and antennas), and we design/use a noticeable long 50 ohm trace/cable in between. If I recall right, this design ...
1 vote
59 views

Vector Network Analyser (VNA)

I am trying to achieve impedance matching using load-pull mechanism and I recently found out that on a Smith chart in the VNA, the S21 doesn't make any sense as I have to plot transmission parameters ...