# Questions tagged [input-impedance]

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### Input resistance of an instrumentation amplifier [closed]

I have a following problem: Calculate the input resistance of an instrumentation amplifier in the circuit given below I also need to change the circuit so that the differential output signal becomes ...
53 views

### Output-Z (electret) higher than Input-Z (preamp)

What happens if an electret microphone capsule (JFET in catridge) is connected to a preamp with considerably lower input impedance than the capsule's output impedance itself? ECM output Z: 2.2K Preamp ...
69 views

### NE5532 as a Guitar Pedal Buffer

I’ve been trying to better understand the NE5532 and wanted to try designing some circuits with it. I wanted to do a dual-supply non-inverting guitar pedal buffer, but I’m concerned about the input ...
94 views

### Complex Input Impedance of Autotransformer with Complex Load

I am interested in the input impedance Zin of an autotransformer with coupling k and complex load Z1 as shown in the picture. Does anyone know how this can be calculated? This is what I tried so far. ...
62 views

### RF amplifier class A

I have simulated a class A RF amplifier. When I simulated the output impedance, it is around 50 Ω for the frequency range that is of interest (50 kHz to 100 MHz), now at the input impedance is around ...
55 views

### What is the standard form for writing the second order transfer function for Input impedance?

When writing the transfer function for a system, the Characteristic equation in the denominator which carries information about the poles of the system is equated with the standard second order ...
1 vote
51 views

### What is the resistance of this equivalent-circuit?

In order to cofigure an ADC, I need to know the input resistance to the ADC Pin of a uC, designated as R_source in the following equivalent circuit: From ...
1 vote
48 views

### Computing input resistance of two common-base configurations

When computing the input resistance of this common base configuration, the collector current $I_C$ is approximated as equal to the emitter current $I_E$: simulate this circuit – Schematic ...
92 views

### Does high pin impedance affect the need for resistors?

I'm designing a brushless motor controller as a hobby project. I'm using the MP6538 gate driver (datasheet here: 1), and I have some questions about pin impedance and whether or not resistors are ...
45 views

### Can I pull down with 5V logic a not-level shifted (which is at 2.8V logic pulled-up) input? How to pull it up to 2.8V again, with no level-shifters?

I have a Distance sensor which has an enable pin (XSHUT pin in the diagram) which is pulled high in its own PCB module at 2.8V, to enable it to work. My Attiny85 MCU, which controls the sensor, is at ...
209 views

### How to derive transistor input impedance?

Given the following circuit, When Ro is not infinite, from the book, ZB is given as, However, when it's infinite, the input impedance is easily obtained as the parallel combination of RB and β(re+RE)...
81 views

### Transistor Re Model Input/Output Analysis

I have been trying to derive Av , Ai , Zi , Zo from a two port system model of a transistor. I know that the input voltage must be the voltage at the base to ground, and the output is from collector ...
47 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 ...
1 vote
99 views

### Input resistance of an inverter op-amp circuit

I need to find the input resistance of this circuit. There are two parts of this exercise: The first one is to find the input resistance of the circuit without the capacitor. The second is to the ...
1 vote
124 views

### Input resistance of an op-amp circuit

I need to find the input resistance of this circuit. There are two parts of this exercise: The first one is to find the input resistance of the circuit without the capacitor. The second is to the ...
45 views

### What is the difference between these two input impedance equations?

I'm currently solving some university E&M homework problems and to solve input impedance, we were given this formula (from Fundamentals of Applied Electromagnetics 6th Ed): But when I browse ...
1 vote
219 views

### How to buffer (high input impedance required) a differential signal

I'm wanting a to increase the input impedance to a differential ADC. The ADC spec states that it can't handle a negative voltage lower than -100mV the ADC's supply can handle ~5V (this is a ATtiny1617)...
81 views

### How can I get the input impedance of this multistage amplifier?

I was trying to figure out the input impedance of this multistage amplifier. The input impedance of the other stages can be simplified to $R_{i2}$. I tried to replace T1 with the hirbid model but ...
74 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 ...
53 views

### Impedance of antenna and noise propagation

I would like to better understand how noise is radiated. Suppose the circuit under study is a circuit with a DC/DC converter (source of noise) and an analog circuit (receiver) which is very sensible ...
44 views

### Input impedance when an opto-isolator is in series

My circuit is detecting 24Vac/dc signals with an opto isolator at the input. HCPL354 is the opto isolator and I am adding 4.4Kohms resistance in series to limit the current. When I make the datasheet ...
140 views

### Measuring variable impedance

I was wondering how to design a measurement system that's able to correctly measure a load impedance that can vary over time and can possibly have very low as well as very high values (see figure ...
73 views

### When should an unmatched antenna be measured with a cable length in even multiples of a half-wavelength?

A few years ago someone told me that if you use a cable which has a length of an even half-wavelength multiple for the frequency being tested, then the impedance measured at the end of that cable will ...
685 views

### How to lower input resistance of buffer (unity-gain) op-amp?

A practical op-amp connected in a unity gain configuration will have a very high input resistance (mega-ohms or higher). How can I add an external resistor to modify the input resistance to the kilo-...
43 views

### ADC input impedance - DC682a with sensor

I need to read sensor position with 16 bit resolution, with this spec: I currently have in hand the DC682A ADC, but Im not sure if I can use it from datasheet LTC1859: "The input impedance is ...
137 views

### Input impedance of op-amp

How can I calculate the input impedance of this circuit?
58 views

150 views

### solving purely resistive DC circuit using input output impedances and gain

I want to solve the following example circuit not using node analysis or other methods but calculating input impedance/output impedance and gain of the circuit. The circuit has no AC source and is ...
114 views

### S-Parameters Power amplifier impedance matching

I recently decided to conceive a 10W class 446MHz amplifier. I want to be able to amplify a 100mW signal into a 10W, for that i'm going for a two stages amplifier : SKY65162 to amplify the signal to ...
113 views

### Lossless quarter wavelength transmission lines

so my lecturer released a past paper with the answers and I have no idea how he got the answer to this question. Please could someone explain it to me? Thanks. The question is: A lossless quarter-...
1k views

### What is this circuit called, and what is it used for?

I analyzed this circuit and found that it's an inverting amplifier and that the impedance of the circuit goes to zero when the frequency of the input voltage goes to infinity. Does anyone know the ...
65 views

### Amplifier with bipolar transistor

What does input and output impedance (I/O) in electronics mean? This is in my book but I didn't understand it. Please explain it to me
1 vote
223 views

### Define input impedance of a buck converter for ideal converter (efficiency 100%) & practical converter

What I know was -The input impedance by the closed-loop buck converter in CCM mode, Zi and, in turn, that presented impedance is dependent on Zo and the duty cycle used by the buck converter below is ...
901 views

### Explanation about op-amp bias resistor and bootstrapping

I am reading a book on op-amp and its applications in linear-integrated circuits and came across this topic of creating an op-amp circuit with very high input impedance. I believe that I understand ...
1 vote