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Old 2nd October 2014, 06:47 PM   #1
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Default Class aP amplification

The letters aP in Class aP stand for analog Pulse; which characterize operation of this type of amplification. The goals, and proposed merit/value of Class aP will follow as I explain its operation, and undoubtedly from your input.

The generator of analog pulses is the Precision Rectifier [PR] shown in the schematic of the attached image. Here is how it works:
1. The operational amplifier [OA; actual is 1/2 LF353N] inverts sinusoidal input signal Vi.
2. OA has two independent and identical feedback branches emanating from its output and terminating at its inverting input.
3. Each feedback branch has a rectifying diode [actual 1N914].
4. By example of operation, allow the voltage of the shaded part of input signal Vi to increase. It follows that OA creates an inverted version at its output.
5. This step reverse-biases diode D+ of the upper feedback branch, and thus prevents input current [from the sine-wave generator] to flow through it.
6. The instantaneous voltage of the shaded input signal, and the value of input resistor R determine the value of input current moving from the sine-wave generator in the direction of the inverting input of OA.
7. This instantaneous input current [substantial in value] cannot flow in the inverting input of OA because this physical input has a high input resistance. It also cannot flow in the upper feedback branch because D+ was immediately shut off as mentioned in step 5.
8. However, this input current readily flows in the lower feedback branch because OA facilitates it by forward biasing diode D-; by using its important purpose to force zero Vdc or a virtual ground at the inverting input so as to match the actual value of zero Vdc ground of the non-inverting input.
9. Virtual ground is the electrical center point of the shaded parts of the input signal and the shaded output pulse. Both must be out of phase, and have equal;but opposite values for their voltage. This is an informal mechanism used to generate a negative pulse at output B.
10. A similar informal mechanism can be used to generate a positive pulse at output A.
11. This Precision Rectifier cuts the sinusoidal input signal [Vi] into two electrically independent mono polar pulses. Each pulse from this point forward will be processed separately. But both pulses must be processed simultaneously and identically in real time so as to recreate later on the original analog sinusoidal signal as faithfully as possible.
12. The analog pulses at the output A and B begin and end as close to zero Vdc as allowed by OA. This precise dual half wave rectification means that it is repeatable; but one needs to mind its accuracy which has to do with the faithful replication of each pulse regarding its parent portion [shaded and not] in the parent sinusoidal input signal Vi.

The next post will show a concept Class aP amplifier.

Best regards.
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Old 2nd October 2014, 07:02 PM   #2
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I think this is Sandman class S - a circuit that splits the signal in a pos and neg portion for two output halves.
It was done with current steering; your circuit does it with voltage steering. Nice case of thinking out of the box!
You should build it, see how well it works.

Your example is with a sine wave but generally the signal is not a single sine so it is better to speak about signal splitting than 'pulse' amplification.

Edit: not Sandman class S - I will look it up.

Edit edit: A new approach to Class B, part 1 & 2, Peter Blomley, Wireless World, february/march 1971.

jan
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Last edited by jan.didden; 2nd October 2014 at 07:10 PM.
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Old 2nd October 2014, 07:55 PM   #3
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Quote:
Originally Posted by jan.didden View Post
I think this is Sandman class S - a circuit that splits the signal in a pos and neg portion for two output halves.
It was done with current steering; your circuit does it with voltage steering. Nice case of thinking out of the box!
You should build it, see how well it works.

Your example is with a sine wave but generally the signal is not a single sine so it is better to speak about signal splitting than 'pulse' amplification.

Edit: not Sandman class S - I will look it up.

Edit edit: A new approach to Class B, part 1 & 2, Peter Blomley, Wireless World, february/march 1971.

jan
Thanks Jan for your comments. I have already assembled/hard wired a dual half wave precision rectifier. I am using it in an audio power amp application for assessment. I'll gladly share all as I planned in future posts [soon] after I give additional details to further explain this approach. In reality, this approach [be it called signal splitting as you suggested, or Class aP] is operationally far from Class B; but actually one that I may call "Pulse A". The reference by Blomley is relevant to see.
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Old 2nd October 2014, 09:31 PM   #4
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Default Concept Class aP amplifier

A simplified schematic of a Class aP amplifier is attached for discussion. It is in two functional parts. The precision rectifier of Post #1, and a complementary bjt power output stage demonstrator. As written, this output stage gives a trans conductance or current source power amp. Each bjt is given a mild forward bias [variable battery at base]. Here is how this amp works.

1. As the sinusoidal input voltage provided to precision rectifier goes positive [shaded], a negative rectified or pulse signal emerges at its output port B, and is presented to PNP transistor.
2. PNP amplifies shaded pulse and shows it at its collector.
3. During the time interval [0 to t1 seconds] of the start to the end of shaded negative pulse, NPN sat idle unaware of the operation of PNP. NPN did not cut off or crossover; because it was not allowed to do so.
4. At the end of time t1 of sine-wave signal, PNP returns to idle state, until a future negative going pulse comes its way for processing
5. At time t1, a positive pulse emerges at the output port A of precision rectifier.
6. It is solely presented to NPN which amplifies it during the allocated time interval of t1-t2.
7. The electrical joint at the power output [opposed collectors] splices both halves [or pulses] so as to regenerate an amplified replica of the sinusoidal input signal Vi.
8. The important result is that the bjts operated independently, equally, and were not allowed to "crossover" into each other's electrical regions of operation.
9. The business of "crossover" in Class AB power amplifiers was denied to its complementary devices; because it has already been accomplished/managed [with high precision] in the preceding line-level Precision Rectifier.
10. Point 9 above gave a clear purpose for the precision rectifier, and a clear performance objective for the power output stage.
11. Thus, each bjt is always on and operates exclusively in pulse mode A mode ; because it was denied cut off on purpose by this approach of amplification.

more forthcoming...
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Old 3rd October 2014, 11:25 AM   #5
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no matter if it has been tried before
i really like the way you think

btw thx for the ref jan!
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Old 3rd October 2014, 11:50 AM   #6
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In fact it is about as pure class B as you can get; exactly 180 degrees duty cycle. Now the marketing dept. may have another idea about that, I understand that

jan
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Old 3rd October 2014, 12:28 PM   #7
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Default Class-aP

I really like the way you have started the topic by explaining it in a simple way.
Also many thanks for introducing us to such novel, out-of-the-box concepts.

I am looking forward to reading it completely.

Thanks!!
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Old 3rd October 2014, 12:52 PM   #8
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Heh in any marketing department I know of this would be called class A ... Why because neither transistor switches off so they're both on 360 degrees of the sinusoidal input
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Old 3rd October 2014, 12:54 PM   #9
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Blomley amp
Hartsuiker amp
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Old 3rd October 2014, 12:59 PM   #10
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Franz thanks for that Hartsuiker amp - never saw that before.

Jan
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