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46 views

Lower noise in biased op amp

I have a circuit similar to this. I’m trying to lower my noise under 60 Hz. Using pspice I keep finding that I need a very large resistor for R5, like 50 gigs but in practice this is not giving me the ...
0
votes
0answers
36 views

What would be the difference in the voltage transfer curves of this two circuits, assuming the op-amps are not ideal?

How does the resistor connecting the non-inverting terminal to ground affect the transfer curve?
0
votes
0answers
52 views

How to solve practical OPAMP with finite differential resistance and finite offset current while other parameters can be considered ideal?

simulate this circuit – Schematic created using CircuitLab Ip(bias)=200nA rd=differential resistance=5Mohm a=infinite What should be its output? I am confused if I should consider negative ...
0
votes
2answers
185 views

In an AC coupled Op-Amp circuit where do input bias currents flow from?

If we have an AC coupled amplifier like the one below, i've read and been told it needs a DC path to ground to allow input bias currents to flow, though I just can't get my head around this, I bias is ...
0
votes
1answer
64 views

Bias resistor in opamp circuit

For the circuit below, what is the purpose of the 2 bias resistors. They are said to detect breaking, what does it mean.
0
votes
2answers
107 views

Need help to increase schmitt trigger sensivity in a circuit

I need help on a circuit I've designed to detect hits on a piezo sensor on a drum. It uses an opamp with 2 channel, on goes to a schmitt trigger, the other to the ADC input on the XMEGA ...
1
vote
1answer
349 views

Input bias current compensation

I am studying the Input Bias Current compensation technique by connecting the resistor to non inverting terminal of opamp. why the reistor of bias compensation should be parallel value of Rf & Ri ?...
0
votes
1answer
150 views

Attenuator with strong bias

I am trying to come up with simplest solution to reduce 0~2.5V DAC output to 0.09V swing and shift it into -19.34~-19.25V range for controlling current limit of OPA548 op-amp within 0~100mA. There is ...
0
votes
1answer
126 views

Amplifier Causing Problems When Observed at DC

INTRO: Hello everyone! I am experimenting with audio amplifiers for a while now. I learned how to do an operational amplifier with discrete components and understand all its section and sub-circuits, ...
0
votes
1answer
57 views

Input biasing and coupling calculations

I have a low frequency input signal 3-80 Hz that I am feeding into an inverting op-amp input. I am slightly confused as to what values I should choose for the following components - R3, C2, R4: The ...
1
vote
2answers
242 views

Why is a common mode bias required for this differential amplifier? [closed]

TI makes the ADS1118 which is an ADC with a programmable gain amplifier (PGA). In one of their application examples (page 4), they indicate that small differential input voltages (1-2mV) must have a ...
2
votes
3answers
332 views

Single supply op amp to convert 0-5VDC to +/-2VDC (microcontroller to line level)

I am generating a 0-5 volt sine wave using an arduino with a DAC. I would like to level shift this signal (DC bias?) by -2.5 volts and have a gain of .8, so that I end up with a line level sine wave. ...
0
votes
2answers
132 views

Need help with instrumentation amp behaviour

I was wondering if someone could help me understand why this instrumentation amp isn't working the way I think it should. The amp is an INA155. My intention is that at if a voltage (positive or ...
3
votes
4answers
775 views

adding dc bias to my signal

So I am having trouble understanding the following schematic. It is supposed to take an input through the capacitor C6 which is an AC sine wave and add a DC bias to it. However I do not understand how ...
0
votes
2answers
138 views

Why is this resistor connected in such way?

Why is the R2 resistor connected to bias instead of ground? As far as I know, only one of the op-amp's inputs has to be biased, so why such configuration? Also, how does this affect the gain? Edit #1:...
0
votes
2answers
111 views

Another solution for all MOS are in cutoff saturation region

Here is a two stage amplfier with a beta multiplier bias(lab3),the schematic of lab3 is in the second picture. I simulate them when VDC is 1.8v and 1.98v for tt-corner and ff corner in 25 degree ...
4
votes
2answers
550 views

MOSFET H-Bridge Amplifier Unbalanced Gain

I have been designing a 100 watt, high frequency (20 - 40 kHz), bridged amplifier using MOSFETs. Although I have some systems and electronics background, the behavior of the MOSFETs is a bit beyond my ...
0
votes
1answer
271 views

DC biasing arrangement in this audio phase shifter circuit

The circuit is composed of four phase shift opamp stages each with a JFET used as a variable resistor. Part of the circuit I do not understand is the DC biasing arrangement. I can see that it uses a 4....
1
vote
3answers
1k views

Opamp input voltage divider creates wrong voltage - what could be the cause?

I'm using above 1:2 differential opamp, when 72V applied to the 30:1 voltage divider, voltage across R1 is only 1.727V instead of 2.4V, opamp output is around 3.4V. Opamp is LMC6062IN/NOPB http://...
0
votes
3answers
767 views

Maximum DC offset voltage

I want to calculate the maximum offset voltage of this circuit: Here's what I did so far: Ib is the bias current and Av is the op amp gain. My question is, how can I do what is asked without knowing ...
3
votes
1answer
346 views

Op-amp bias issue to to charging of DC blocking capacitor

We're using the above circuit to drive a sinusoid with constant current into a custom sensor which is best modeled as a series capacitance & resistance (~100ohm, 1uF). The op-amp is single supply, ...
0
votes
3answers
649 views

Can I use one voltage divider to bias multiple points in circuit?

I have 4 nodes in my circuit that require virtual ground of half the power supply voltage. 2 of the nodes are just offset for input signal and other 2 are for op-amp biasing to virtual ground. Can I ...
0
votes
2answers
224 views

Non-inverting-Amp bias current: understanding output error

I have a book (Tietze, Schenk: Electronic circuits) that shows this equivalent circuit of a non-inverting amp. \$I_B\$ is the bias current, \$I_o\$ the offset current (difference of bias currents). ...
0
votes
2answers
257 views

Op-Amp Input Bias Compensation for Multiple Feedback Filter

I'm adding an input bias current compensation network to the positive op-amp input of my band-pass multiple-feedback filter. I'm setting the source impedance for the positive input pin equal to that ...
3
votes
3answers
461 views

500V unity gain buffer

I am currently in the process of designing a high-voltage bias supply for use with an ionization chamber. The voltage source itself is taken care of however I need a unity buffer to drive the guard of ...
0
votes
2answers
220 views

Bias voltage of non-inverting op amplifier drops to 0 when input signal connected

I am working on a non-inverting opamp amplifier, using OPA2134, to amplify the 150mV peak signal (1 kHz sine wave playbacked) from a phone audio jack to ~4V peak sine wave, that drives a LED using a N-...
2
votes
2answers
2k views

MOSFET voltage follower for non-inverting op-amp biasing

Question is based on this document. Quoting from there: Voltage Follower Biasing: This method is exactly the same as the voltage divider biasing, except it uses an op-amp (or transistor) to ...
0
votes
4answers
1k views

Where does an op amp's input bias current come from if capacitor is used?

In the case of a non-inverting amplifier, if I DC couple the input signal with a capacitor only, \$C_1\$ (i.e. no resistor to ground), sources (as well as an experiment in the lab) show me that the op ...
2
votes
2answers
5k views

Operational amplifier parameters: Input bias current, Input offset current, input offset voltage

I've been reading about input offset voltage, bias current, and current offset for a few days now and still can't get some things straight. I'll summarize what I understand and then pose the ...
0
votes
1answer
336 views

Bias current and offset voltage, op-amp 741 DC imperfections [closed]

Can the effect of the bias current counterbalance the effect of offset voltage? I am asking this question because today in a lab it occurred to a couple of groups. Is there a reason for that?
1
vote
1answer
213 views

Does an op amp needs an Input Bias Current to operate? [duplicate]

I'm confused about the source of Input Bias Current, is it generated by op amp, where the current "leak" from the op amp. or it's a must to operate the op amp? for example if I have in a data sheet a ...
2
votes
1answer
638 views

Changing a signal's DC offset before amplifiter and ADC

I'm trying to feed an audio signal which has around 5v DC bias to an amplifier and then an ADC. the final signal should have 2.5v DC bias. i've mixed things i've learned off forums but i'm still not ...
2
votes
1answer
2k views

Any tips on designing an audio preamplifier for low frequencies?

I'm currently trying to design an audio preamp with the purpose of amplifying very faint audio signals (possibly in the microvolt range) from 20-200Hz. I've tried both transistors and op amps for ...
2
votes
2answers
247 views

Resistor on pin 3 of a Log Amplifier

I'm trying to understand what's the function or R2 resistor in this transdiode log amp configuration. I suppose I've to match the right value to give in order to minimize the effect of input bias ...
0
votes
1answer
55 views

How would adjusting the bias on an op amp effect the signal?

I am using an op amp to boost an audio signal. The bias, it appears, is typically half of the input voltage. What kind of effect would it create if the bias was to be adjusted up or down? Would ...
0
votes
1answer
308 views

Opamp circuit has an unintended DC bias

I was fiddling around in LTSpice for a project I'm working on. This circuit is a basic preamplifier and a low-pass filter. But this question refers solely to the amplifier stage. The opamp is the "...
0
votes
1answer
46 views

Drop on high pass filter measure

So I'm implementing an analog control scheme, and one important component is a first-order high pass filter. The source signal is the output of a shunt monitor (INA138 - in the circuit below the ...
0
votes
2answers
184 views

Input Biased Compensated Op Amps

I was reading about the Input bias currents for an op-amp. And I had a question regarding the ones internally compensated for. So in general if I was to use an Op amp for any particular application ...
1
vote
3answers
2k views

Controlling audio signal with digital potentiometer

I am very confused about how to go about using my digital potentiometer to control an audio signal. I have a MCP4231 digital pot and I would like to use it as a MCU controlled variable resistor for ...
2
votes
2answers
323 views

Shared bias voltage for quad op-amp

I'm pretty inexperienced in EE, but I'm adapting the circuit given in this question to amplify microphone inputs to drive an ADC. I am going to be driving 4 ADC channels (on a Beaglebone Black) from ...
1
vote
1answer
251 views

Opamp: amplifying DC bias problem in output?

OpAmp beginner here. I'm trying to do the simple 1KHz, 1V p-p sine wave amplification circuit using TL071 or similar OpAmp. Simulation currently in LTSpice. I've biased the VCC to half to try to ...
-1
votes
2answers
667 views

Why is a 0V DC point at the output of an op amp critical for feedback?

I am designing an op amp that consists of an active loaded single ended output differential amplifier that is connected to a buffer stage and then an output stage. When the input signal is connected ...
1
vote
2answers
608 views

The direction of the bias current of LM311

I thought the conventional method to denote the direction of the bias current is to precede the IIB parameters with the '+' or '-' flag in the 'electrical characteristic' table, '+' indicate the bias ...
0
votes
1answer
146 views

why 2 input bias currents are equal for OpAmp?

In Floyd book it says that 2 input bias currents for 2 inputs ideally equal. I understand if they are equal in a common mode, but how they can be equal in a differential mode if in this case, one ...
2
votes
2answers
770 views

Bias DC signal from op amp

I've built a DC signal mixer that doesn't quite work as expected. The supply voltage is 9V, virtual ground at 4.5V and the mixer uses a TL074 quad op amp. While the input voltage is 0-9V, the output ...
2
votes
2answers
4k views

Driving hard drive voice coil actuator with PWM

I have been trying to control a voice coil actuator with PWM input, but i have the following problems and would like you to correct or point me in new directions. I have an arduino which outputs PWM ...
23
votes
1answer
53k views

What's input bias current in opamps?

Is it the current you have to drive in the input to get a specific, defined voltage at the output? And don't the currents cancel each other when applied to both inputs?