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  1. #1
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    Amplification by addition, can be considered as amplification?

    Hi, all amplifiers I am aware of, "modulate" the power supply voltage/current at their output. The amount of "modulation" is controlled by the lower level signal at their input (base for a bjt, gate for a fet etc).

    In other words, the original signal waveform is not touched at all. It just drives the transistor, so that it can modulate the PSU voltage/current and create an amplified replica of the input signal.

    Now, I thought about the phasing of two signals. If two signals of equal phase are fed to an adder, one adds to the other to produce a higher level signal. As I think this, this process actually "touches" the input signals. In other words it performs direct manipulation on these. Can't it be considered another form of amplification?

    I am sorry about my non-technical terms.
    Professional engineering is the top, but amateur engineering is more fun.
    It is when you cross the barrier between these two, that things become really fascinating!

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    Re: Amplification by addition, can be considered as amplification?

    Hi,

    amplifiaction is multiplication.
    Adding is not amplifiacation.

    If two signals of equal phase are fed to an adder, one adds to the other to produce a higher level signal.
    This is only true for sine signal (At least I canīt think of another signal wavefrom), therefore it is an exception.

    You canīt do this with a mixture of sine, you canīt do this with square wave, you canīt do this with triangle.....


    Klaus



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    Re: Amplification by addition, can be considered as amplification?

    I don't agree. Multiplication is an iterate addition:

    3*5 = 3+3+3+3+3 or 5+5+5

    then if you sum up N times the same signal (sum in-phase signals) you multiply by N, regardless from the waveform, that is the same of using an amplifier of gain N.



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    Re: Amplification by addition, can be considered as amplification?

    For the present discussion, it's reasonable to define amplification as power gain. The discussed "adder" can be respectively identified as power combiner.

    Adding or combining two RF signals can form a single signal of higher power. But what's the source of both signals? If you have a single input signal, you'll need a power splitter and an amplifier to form a second signal to be combined with the first one. Or you have already two input signals and combine them. There's still no power amplification, the total output power is smaller (or at best equal) to the total input power,



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    Re: Amplification by addition, can be considered as amplification?

    Hi,

    @albgg:
    You are correct, but not in general, but as a special case.
    With special cases you can explain almost anything.

    *****
    Imagine a black box. It is an amplifier.
    * One input is the (varying) signal "S"
    * One input is the somehow fixed gain "G" (volume)
    It has one output "O"

    Then the amplifier (or multiplier) has the mathematical formula: O = S x G

    Example: let's say the input "S" changes: -2 / -1 / 0 / 1 / 2 (maybe volts)
    Lets say gain is 4.25. (it has no unit)
    The output is: -9.5 / -4.25 / 0 / 4.25 / 9.5 (volts)

    If gain is set to 1.5:
    The output is: -3 / -1.5 / 0 / 1.5 / 3 (volts)

    With a multiplier (or amplifier) if one input is zero, then the output is zero, too.
    If signal input of an amplifier is zero, then the output is zero.
    If the gain if an amplifier is zero, then the output is zero, too

    *****
    Now a adder. The mathematical function is: out = A + B
    One input of an amplifier is surely the signal input,
    The output is surely the signal output..

    But your solution has a couple of adders: let's say gain = 3 and signal = 5.
    The you have two adders: 5 + 5 + 5...
    Hiw many adders do you have with a gain of 4.25?

    ****
    An example for an adder is when you make a mono signal from two stereo signals.
    M = R + L. Two inputs, one output.
    All have the same unit (volts)
    If R = 0, then the output is just L...

    Klaus



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    Re: Amplification by addition, can be considered as amplification?

    Now, I thought about the phasing of two signals. If two signals of equal phase are fed to an adder, one adds to the other to produce a higher level signal. As I think this, this process actually "touches" the input signals. In other words it performs direct manipulation on these. Can't it be considered another form of amplification?
    This reminds me of a "distributed amplifier" where the same input drives multiple amplifiers that have the outputs combined.
    Click image for larger version. 

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    This is a very powerful technique used to make very wideband amplifiers of high power especially at microwave frequencies.
    Cheers, Tony.



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    Re: Amplification by addition, can be considered as amplification?

    I agree with FvM. In case of an RF amplifier it makes sense define amplification as power gain. In this case adding is not the same as multiplying
    But more in general we can also consider voltage gain

    Quote Originally Posted by KlausST View Post
    Hi,
    Hiw many adders do you have with a gain of 4.25
    Klaus
    You can sum signals having different level (same phase) in order to obtain non integer gains.



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    Re: Amplification by addition, can be considered as amplification?

    In the context of RF amplifiers, summing or adding refers to passive circuits where Pout <= Pin. Amplification applies to cases where Pout>Pin.

    The OP describes first an amplifier using a high level modulation technique, as often seen with switchmode amplifiers. I typically view these not as amplifiers, but as mixers, with the low power RF input being the LO port.



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    Re: Amplification by addition, can be considered as amplification?

    Hi,


    You can sum signals having different level (same phase) in order to obtain non integer gains.
    I agree: in formula this means: out = input + (input x A) or formed as : out = input * ( 1 + A).

    Then the question is: How do you get "different level" without a multiplier?
    And: doesnīt mean "different level" that there already is an amplification? ...with gain smaller or larger 1?


    Klaus



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    Re: Amplification by addition, can be considered as amplification?

    Quote Originally Posted by KlausST View Post
    Hi,
    Then the question is: How do you get "different level" without a multiplier?
    And: doesnīt mean "different level" that there already is an amplification? ...with gain smaller or larger 1?
    Klaus
    For instance using two DACs connected to a uP: the first one fed by datas generating a signal of amplitude A, the second one of amplitude B. Same waveform, same frequency same phase.
    However I understand it's useless in practice. I though the discussion was more at a, let me say, "philosophical" level rather than practical applications.


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    Re: Amplification by addition, can be considered as amplification?

    Quote Originally Posted by albbg View Post
    I though the discussion was more at a, let me say, "philosophical" level rather than practical applications.
    Indeed...
    Hm.. This makes me think of a possible application though. If I have a microcontroller, producing square waves of the same phase in all its pins (configured as outputs), Can't I add them together and have a larger amplitude square wave, than the micro can give (0-5v)?
    At post #2 it was mentioned that you can't do this with a square, but why?
    Professional engineering is the top, but amateur engineering is more fun.
    It is when you cross the barrier between these two, that things become really fascinating!



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    Re: Amplification by addition, can be considered as amplification?

    Hi,

    At post #2 it was mentioned that you can't do this with a square, but why?
    I think this was not my day.

    Somehow in post#2 I imagined two signals with equal amplitude buf varying phase... I was wrong in this.
    * for sure two signals with equal phase can be added and the waveform remains the same. (without knowing HOW to add them)
    (And yarying the output amplitude by adding two signals with different phase works on sine, but will change waveform with other than sine)

    ***
    But to the problem with the microcontroller ports: I canīt imagine a circuit thad is able to add the voltages of a port output to a higher result voltage.
    .. you surely donīt want transformers.
    .. and you donīt want it to work like a bootstrap circuit (diode, capacitor) .. similar to a Cockroft Walton multiplier
    .. you may use two outputs in bridge mode. This may increase the differential voltage, but not the absolute voltage. (wrt GND)

    Klaus



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    Re: Amplification by addition, can be considered as amplification?

    I am sorry about my non-technical terms.
    Respectively part of this thread implements a vague talk about "adding signals" without referring to signal parameters and circuits.

    A good clarification has been made by mtwieg:
    In the context of RF amplifiers, summing or adding refers to passive circuits where Pout <= Pin. Amplification applies to cases where Pout>Pin.
    The distinction can be also applied for low frequency circuits. Voltage enhancement can be achieved without external energy sources as long as Pout is <= Pin. Possible circuit are transformers and all kind of switchers with capacitive or inductive energy storage.

    Adding the output signal of multiple pins can be easily done, a simple parallel connection multiplies the signal current. That's neither signal amplification, just bundling existing signal power.



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