Connected how? Through power combiner?
Both amplifiers fed by the sample input signal?
Hi,
can you give me a hint where in the document are "two amplifier outputs connected together". I don´t want to read the complete document.
Klaus
Hi,
I think I´m blind: I can´t find it.
My section two just is named: "2 Signal-Chain Considerations".
No further text.
Did you upload the correct document?
Klaus
In principle if their inputs are also the exact same signal, it can work. But in practice it will lead to awful performance if there's any mismatches. Splitters and combiners are used to do this while isolating the inputs/outputs from each other.
Hi,
now it is the correct document.
And you can see that the outputs are connected using resistors "Rs"
The document says:
In high voltage swing applications, where an operational amplifier is pushed to drive close to
its supply rail, it is possible to drive several identical operational amplifiers in parallel and
combine the outputs to achieve higher bandwidth and lower distortion. The remainder of this
design guide develops this concept of load sharing and demonstrates how this technique can
be used to reduce current sourcing and sinking requirements towards the amplifier.
Also they speak about amplifiers in the 60MHz region. What else do you want to know?
Klaus
I think the references to OPs are basically inappropriate because OPs are voltage sources in contrast to RF amplifiers that implement impedance matching with a defined output impedance, e.g. 50 ohm. The paper is about load sharing of OPs, performed with lossy resistive networks. It should be discussed under Analog Circuit Design rather than RF and Microwave.
Paralleling 50 ohm RF amplifiers results in halving the output impedance to 25 ohms, which may be intended in special cases, but usually requires an impedance transformation to match a 50 Ohms load. A power combiner (e.g. Wilkinson) does the transformation with additional isolation of amplifier outputs against each other.
If RF amplifiers can be paralleled without harm is also a question of power level. In case of high power amplifiers, you often use circulators to isolate the load and avoid possible amplifier damage by reflected power. They also make parallel operation easier.
Thank you for the details. For example, I'm using low power amplifiers that has output power of 4 dBm in CMOS 180 nm technology and I don't want to install external components such as power combiers and circulators at the output. Does this application falls under the special case if the power amplifiers are not damaged?
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