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DC biasing is the same as "bias voltage". basically all electronic devices need some voltages set so they work correctly, this is what the bias does. DC offset this is a when some terminal of an electronic device has some DC on it which can be an advantageous or disadvantageous. For example you may have an amplifier who's output terminal is meant to at earth potential, but due to component tolerances is sitting at some DC voltage. This is called a DC offset. If you connected a loudspeaker there would be a loud "plop". So you arrange for a DC offset to be put at the input of the amplifier to get its output to 0 volts.
DC coupling is when an amplifier can take a DC voltage as an input and amplify it. It requires special techniques to over come drift with temperature.
Frank
dc biasing means to establish the dc operating conditions for a circuit, i.e. to ensure proper voltage or current under certain conditions. dc offset means the dc voltage level on which another voltage is superimposed. dc offset is added to circuit for desired operation. dc coupling is just coupling a dc voltage with next stage of circuit e.g. an amplifier. it is usually directly coupled.
Galib
Attached is the circuit, with +ve and -ve voltage but still biased, so is it a correct? My other question is when bias by 2.5V what could be the amplitude of the signal if a signal of 5 V amplitude is applied to the input (is it going to be 7.5V)? Also is my understanding of biasing correct based on the attached waveform.
Yes, everything OK - provided you want for some reason that the amplified signal at the output rides upon a dc level of 2.5 volts.
If not (that is the normal case) you should drop the voltage divider at the pos. input.
If capacitive input coupling is required, provide a (large) resistor beween pos. input and ground for dc bias current.
My microcontroller has an ADC of 5V (0 to 5V). The input signal is 25 mVpp. And I want to amplify it to 5V.
1) So I need an amplification of 200. (gain = 5000/25), right?
2) I need the amplification circuit to be powered by battery and should be portable. So, should I use single supply or dual supply using battery?
3) If I am using single supply, at which voltage should my biasing be and what should my +Vcc be? (I need output 5 Vpp, when the input is 25 mVpp)
Op-amps need some head room, because the output signal can't go as positive as the + rail and as negative as the - rail or earth, as in this case. So it would work on a 6V supply but I would use a 9V supply and adjust the bias for the output to sit half way, 4.5V, so the signal can go +- 4V, even though it should only go +- 2.5V. Just use the circuit you showed us with R2 = 200K (not sure you can get 201K)
Frank
I can see that your input is an AC signal sitting on a DC offset. In order to amplify the AC signal, you need to subtract the DC offset first (with an OpAmp). Once the DC offset is gone, you can amplify the signal with another OpAmp.
You need to have a positive and negative rail for the OpAmps ( +/-5 volt might be good enough depending on what kind of resolution you want. If higher resolution is desired, use +/- 9 volt instead ).
To answer second part of you question, you can either use single or dual supply.
With dual supply, you can just connect the positive and negative supply to the OpAmp.
With single supply, you need to use an IC to generate negative voltage for the negative rail for the OpAmp.
I recommend using dual supply if you are allowed ( just an extra battery ).
As for how much gain you need, just use a POT to adjust your gain until you get the desire gain and switch it to a fix resistor after you figure out what resistance you need.
I don't want negative voltage. I want to amplify a signal that goes to a micro controller ADC with 0-5V. So I want a rail to rail op-amp that use single supply so that I can bais it somewhere at 2.5V and still get 0 to 5V using a battery. I have found a couple of op-amps, which are: TLC272, LT1466, LM324N, TLV2771, LM6144. What could be the best choice?
I don't want negative voltage. I want to amplify a signal that goes to a micro controller ADC with 0-5V. So I want a rail to rail op-amp that use single supply so that I can bais it somewhere at 2.5V and still get 0 to 5V using a battery. I have found a couple of op-amps, which are: TLC272, LT1466, LM324N, TLV2771, LM6144. What could be the best choice?
Right. You can put the 2.5V DC offset on the signal again after you are done amplifying it. I don't see how you can amplify the DC offset signal with only a single supply OpAmp because the DC conponent will saturate the OpAmp. Please let me know if you find another way of approaching this problem. :razz:
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