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Real world opamps inputs have small have input bias and offset currents and R1 is meant to balance the impedance at the noninverting input with that seen by the inverting input and reduce the error that would otherwise be introduced.
This won't help with all opamps though since some have very low bias currents that are negligible in most cases, and others ...
6
Assuming you're using the opamp in a feedback configuration circuit, which you probably do because you need some precision.
Also assuming that the voltages at inputs and output of the opamp do not exceed what the opamp can handle at the given battery supply voltage. I'm thinking (common mode) input voltage range and output voltage range with a certain load ...
3
As a kid, I built many a multi-stage bipolar AC_coupled amplifier, using +9v batteries (the big kind, about 3" by 3" by 4"), and the amplifiers always oscillated ----- until I learned to use 5,000uF capacitors on the +9v rail.
In fact, until an uncle suggested VDD filtering using R+C low pass filters like he used in the vacuum-tube receivers he worked with,...
2
You're correct in spotting that that biasing M8 is indeed "tricky".
To bias M8 at the current provided by M7 the only real option is to use feedback.
I can for example use this circuit as a buffer (1x amplifier) by connecting the Vi- input directly to the output Vo.
Let's check that that is indeed negative feedback: if Vi- goes up in voltage, Id(M1) ...
2
As Alex says - any amplifier that provides enough audio output power to drive the speaker and to modulate the LASER adequately will be acceptable.
You can replace the LASER with an LED and lens with surprisingly good results.
For long to very long distances a focused LED is superior to a LASER as the LASER beam self interferes due to its "coherence" while ...
1
I think one solution is the following:
Obviously, it is necessary to calculate the values of the resistors for which, instead of amplifying the signal, it is attenuated for the correct values of the ADC of the MCU.
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Comparators and opamps have high impedance and low current leakage on the input. You can check this by looking at the input bias current in the datasheet. You can think of the input to most comparators and opamps as a resistor having higher than 1GΩ of resistance.
If the opamp/comparator has voltage protection diodes, then the current can increase if the ...
1
TI parts have 1k series internal inputs to limit current to 10mA with 20V.
Rohm parts chose not to include this.
But your 30k series will limit the current to < 1mA.
1
Small primary batteries can supply AC noise current with DC
proof: connect any good 1.5V battery to any speaker and listen to 1/f thermal noise
but Op Amps can reject most AC supply noise (PSRR) but still need attention.
Op Amp circuit designs are usually based on external impedance ratios and not sensitive DC supply voltage with adequate signal common-...
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