# Questions tagged [input-impedance]

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59 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 ...
176 views

### Input impedance of op-amp circuit

All opamps are ideal. The question is to find the input impedance Zin(s). Using KCL: $$I = (V_i-V_{o2})/R_1$$ $$V_i/R_4 = I-[(V_i-V_{o2})/R1 + (V_i-V_{o2})/R_2] -[(V_i-V_{o1})/R_3+(V_i-V_{o1})sC]$$ ...
59 views

### Problem in measuring potential because of oscilloscope's input impedance

I am trying to use a sensor, whose resistance value change from infinity to around 10kΩ when variable load is applied. The load is applied for a small duration and in order to capture that I'm using ...
40 views

### LTSpice - Opamp Buffer Input Impedance Measurement

I tried measuring the input impedance of Opamp LT1128 Buffer using LTSpice. And from the simulation then maximum impedance is showing only 20k. This particular opamp has 300MEG common mode input ...
47 views

### How to improve this circuit design to meet Arduino ADC input impedance requirement?

I have a new pH sensor board, the circuitry looks like this. The Op Amp is operated at 3.3v and the input is "float" to 1.8v with a separate voltage regulator. The output is connected to the ...
233 views

### understanding input impedance theory

The key question is, what is the best or right way to modify input impedance? I am a self-teaching novice at electronics. I'm using the LM386 as a learning platform. Signal input comes from a "...
100 views

### Input and Output Impedance of a TTL NAND Gate

Basically I wanna know how to calculate the input and output impedance of this basic TTL NAND gate I have looked at several books and websites but found nothing useful , can anyone help me please. ...
49 views

### Second order all-pass filter input impedance

I have a question about the second order all-pass filter input impedance when ω = ∞ and ω = 0 and I would appreciate if you could help me to understand the logic. When ω = 0, all capacitors can be ...
57 views

### Input impedance of grounded emitter amplifier with DC feedback

In AoE3 2.3.5.C (page98) it states the following (referring to the circuit in the image): For instance, feedback acts to reduce the input and output impedances. The input signal sees $R_1$ ...
63 views

### Can you reduce audio noise by decreasing input impedance with a resistive load?

First asked this over at sound stackexchange but they pointed me over here as a better place for it. A general question but inspired by a specific example so framed as such. I have powered studio ...
63 views

### How can you find Quality Factor of an arbitrary RLC Circuit?

I'm having a trouble with this circuit. Apparently I know how to deal with a simple RLC circuit but this one is tricky
37 views

### Line input circuit

I'm trying to design an unbalanced line input for an audio device using a single supply. I would like the input stage to provide variable gain between 0 and 2. This is what I have come up with so far:...
155 views

### Trying to understand FPGA input pin impedance

From working with classical microcontrollers, I am used to the fact that pins in input mode appear to have high input impedance - when connecting them to a high voltage, only a small current flows, ...
113 views

### Input/Output Impedance of DC/DC converters and Impedance matching

I am interested in understanding how do DC/DC converters achieve impedance matching for maximum power transfer applications. After visiting this entry, you can see in the "impedance matching" ...
56 views

### UWB circular antenna: input impedance (Zo= 50 Ω)

I'm having difficulty with the line input impedance of the circular planar antenna signal. Its impedance is 117 ohms and the correct is 50 ohms, I am not able to lower the value. I made modifications ...
186 views

### Measurement of s11 with reduced power on NanoVNA

I am developing a 10.7 MHz IF amplifier for a radio receiver. In order to match the input to the output of the driving mixer stage (330 ohm) I need to measure the input impedance. I did the ...
78 views

### Modelling differential amplifier input circuit

I'm trying to understand the behavior of a filter connected between a mixer and fully-differential amplifier. Here are the relevant portions of the schematic. The first part is the mixer output 5VF ...
41 views

### Phase and Gain of transimpedance amplifier and effect of input impedance

I am new to hardware design. I am designing measurement circuit for Impedance Spectroscopy of electrochemistry cell. I need to measure the current coming from electrodes which have range from few ...
75 views

### What does a simple passive circuit to simulate an impedance mismatch look like?

I am trying to learn some of the basics of circuit design. One thing I am curious to make a filter/schematic of is what happens when a voltage source hits an impedance mismatch. eg. A high impedance ...
95 views

### Sziklai pair and Darlington pair input impedence

If i remember correctly the input impedence of a BJT is r_pi=Vt/Ibq. I've read that using those two configurations I get a much higher input impedence. Can someone please tell me why? Maybe some ...
127 views

### What makes a input GPIO pin so sensitive?

I know that an input pin has a high impedance, but how a high impedance makes such pin be so sensitive? According to https://forum.arduino.cc/index.php?topic=454553.0 -- #4 mentioned If the input ...
67 views

### How to integrate current signal to be able to measure it with 50 ohm input impedance of ADC

Preliminaries I am using a photomultiplier tube (PMT) in order to amplify scintillator's light signals. Some of the studied scintillators have long decay time and poor light yield. That makes these ...
68 views

### Why is the input impedance of an emitter follower defined as $\Delta V_{B}/\Delta I_{B}$, as opposed to $V_{B}/I_{B}$?

In The Art of Electronics, chapter $2$:Transistors, page $65$, the author defined the input impedance $r_{in}$ of the emitter follower below as $r_{in}=\Delta V_{B}/\Delta I_{B}$. Why did ...
79 views

### Input and Output Impedances of Differential Amplifier

I have this circuit that is used to convert an incoming analog differential input signal to a single ended signal. The differential input is connected at IN+, IN- and the output is taken from OUT. I ...
119 views

### FPGA input capacitance

I want to estimate power consumption of a battery powered digital circuit that has a CPLD (Lattice LCMXO2-256HC). It receives 64 MHz signal into LVDS input and 10 MHz, 2.5V into a schmitt trigger ...
143 views

### Why does the common collector specifically have a high input impedance?

When looking at a chart comparing different BJT amplifiers, the common collector/emitter/base, it is usually said that the common collector has a high input impedance, therefore it is suitable for use ...
173 views

### How can I interface with arduino mega2560 to detect the presence of a 48 V without pulling down the voltage by more than 0.1 V

How can I interface with a microcontroller to detect presence of a 48 V supply with a source impedance of 10 kΩ without pulling down the voltage by more than 0.1 V? I need to step down the output ...
141 views

### Op-amp input impedance

I was reading the following tutorial from Analog Devices: https://www.analog.com/media/en/training-seminars/tutorials/MT-040.pdf They include the following image and state: In most op amp ...
86 views

### How to match a power amplifier and a loudspeaker array?

I am trying to use a power amplifier that is available to me to actuate an array of loudspeakers. The array has a total number of 30 loudspeakers (ways of connection can vary). And I would like to ...
176 views

### How to find input impedance of this OPAMP circuit?

Assume OPAMP to be ideal with infinite gain (a) and infinite input impedance I am clearly able to see that the input impedance of this circuit is R1 (correct me if I am wrong) but I am unable too ...
99 views

### maximum power transfer explanation

Please provide an intuitive explanation of maximum power transfer. This is a conceptual question therefore I want to ask with an example. I'm wondering in which cases impedance matching is used. For ...
534 views

### Input and Output impedances of Current and Voltage Amplifiers

I read that Voltage Amplifier have high input impedance and low output impedance, and Current Amplifier have low input impedance and high output impedance. If this is true what is reason for this as I ...
2k views

### Why are oscilloscope input impedances so low?

My question is two-fold: Where does the input impedance come from? I'm wondering where the input impedance of your average multimeter or oscilloscope comes from? Is it just the input impedance to ...
247 views

### Input impedance of differential amplifier

Can someone please explain to me, how I should look at the input impedance of the opamps, seen through the voltage $V_1 V_2$? I have two questions on the differential amplifier: Why doesn't the ...
86 views

### Impedance frequency response for a DC motor

Consider the following impedance frequency response for a DC motor : Its equivalent circuit is : Clearly, from the response, there exists a capacitor, inductor, and resistor, but my problem is how ...
66 views

### How do I find input impedance here?

I'm not too sure how to go about doing this. Added what I did so far but I don't know where I messed up.
221 views

### Input Bias Compensation Resistor Calculation for an Integrator

I have been reading the following tech note from Analog Devices that discusses designing an op amp circuit to compensate for the input bias current: https://www.analog.com/media/en/training-seminars/...
258 views

### Impedance calculation from voltage and current (exponential) waveforms

If we want to find the impedance across two terminals (a port) at a frequency $\omega_0$ using the voltage waveform across $v(t)$) and current through ($i(t)$) the terminal, general intuition is ...
601 views

### How are such low op-amp input currents possible?

I understand that op-amps have low input currents; that's one of their defining characteristics. But looking at the datasheet for the LMC6001 (amusingly called an "Ultra, Ultra-Low Input Current ...
1k views

### Strange opamp's output impedance in spice

I'm simulating this circuit in Micro-Cap, which is the clipping stage of a guitar effect. The opamp model is the "NE-5532" I want to measure the input and the output impedance. I expected an output ...
49 views

### Change range of data acquisition system

I have a DAQ with many inputs that can measure within +-10 V, and I want to go up to +-30 V. Using a resistor voltage divider could be an option, but this lowers the input impedance. I would prefer ...
46 views

### Confusion between Input/Ouput Impedance and Thévenin's theorem

I'm bit confused about what Input Impedance or Output Impedance is. I tried to read Wikipedia's page (https://en.wikipedia.org/wiki/Input_impedance) but I find it hard to follow. Is the Input ...
373 views

### Emitter follower and input impedance

I'm designing an active bandpass filter (using only BJTs, voltage sources, resistors and capacitors) with the following properties: Corner frequencies $8 ~ \text{kHz}$ and $800 ~ \text{kHz}$ (...
142 views

### Correct way to calibrate SDR RX into a measuring receiver

While playing with my SDR (Software Defined Radio) Board, I was interested in performing a TX output power table at different center frequencies and TX antenna gains. However, unfortunately, I do ...
77 views

### Calculate input resistance of power amplifier

how can I calculate the input resistance of this circuit? Thank you!
151 views

### Input impedance of circuit

Given current gain (hfe = 100), internal resistance (hie = 2000), reverse voltage gain and output resistance (hre = hoe = 0), compute input impedance for the following circuit. The problem is that it ...
282 views

### Is static negative resistance practically available?

I learned that negative resistance (NR) could be simulated by involving active devices like op-amps and others. I'm interested in the static/absolute NR rather than the differential NR. My question is ...
213 views

### Finding input impedance of the circuit

I'm having difficulties finding complex impedance of the following circuit: What I did first is find the impedance of $C$ and $R$ in parallel, which is: \underline{Z}_{CR}=\frac{R}{1+j\omega CR}...