Is a parallel amp the same as a balanced amp?
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Posted by Frank Raffaeli on May 21, 2008, 3:04 am
Please log in for more thread options > > > Hello all,
>
> > > The differences between a parallelamplifierand abalancedamplifier
> > > is rather confusing. Are they the same, or are they different? Both > > > these circuits, and their advantages, appear to be very close to each > > > other, if not the same... >
> > > Just curious,
>
> > > -Nick
>
> > Parallel refers to the configuration of anamplifier'soutput circuit.
> > And now for something completely different. >
> > Balancedrefers to the nature of the either input or output signals.Balan=
cedmeans that the two lines of the output are referenced to each
> > other and not to ground; the input's or load's voltage is measured
> > between two lines and voltages present on either line (as measured to > > ground) are typically unintentional, undesired and are to be rejected > > as extraneous. This is good for long runs, e.g. between a mic and an > > amp input, because noise is mostly referenced to ground and is so > > theoretically rejected. Whatever noise hits one line also hits the > > other and so is ideally cancelled. >
> > Unbalanced signals are measured to ground, so are limited to short
> > runs where they won't be susceptible to noise pickup, e.g. between > > adjacent audio components. (The run to a speaker is typically long, > > but can get away with an unbalanced line by virture of a speaker's low > > impedance, making it much, much less susceptible to noise. If someone > > went crazy and designed a high-impedance speaker circuit, it would > > benefit from abalancedoutput, too. Nobody's been that crazy yet.) >
> > As you might guess, a mic input, say, that is bothbalancedAND low
> > impedance, is the double-whammy for quietness. Professional mic inputs > > are that way. Cheapo mic inputs are high-impedance and unbalanced, the > > worst case, so they rely simply on short runs to avoid noise. If you > > have to carry signals between two buildings that use separate ground > > systems that may have a small difference between them (or a large one > > if lightning or other surges strike!), then abalancedsystem would be > > preferable so that the signals ignore the ground as much as possible. > > Whole books are written on signals, grounding and noise reduction > > tecniques. Many books. They come with magic wands. >
> Thanks guys for the great input. The "parallel amplifiers" that I > am speaking of are for HF PAs and LNAs, and are in parallel with each > other and have Wilkinson dividers at their input and output. But the > "balanced amplifiers" I have seen are also in parallel, but have a 90=BA > hybrid power divider at their input and a 90=BA hybrid power combiner at > their output. They look so darn close to each other, both circuit- > wise and performance-wise, that it starts to get a bit confusing! > > Best, > > -Nick Sounds like a continuation from the other thread ... An RF balanced amplifier usually refers to a 180-degree phase split, not 90. The main reason to use a balanced amp is to suppress the 2nd (and other even order) harmonics. The main reason to use a 90-degree split is to match the amplifier over a broader bandwidth, and to realize a good match at the optimum noise figure (Zopt). So ... you still didn't answer the question: what linearity do you need? Frank | |||||||||||||||||||
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Posted by TheM on May 21, 2008, 5:59 am
Please log in for more thread options >Sounds like a continuation from the other thread ...
>An RF balanced amplifier usually refers to a 180-degree phase split, >not 90. The main reason to use a balanced amp is to suppress the 2nd >(and other even order) harmonics. >The main reason to use a 90-degree split is to match the amplifier
>over a broader bandwidth, and to realize a good match at the optimum >noise figure (Zopt). >So ... you still didn't answer the question: what linearity do you
>need? Its the same guy looking to build a small pirate TV transmitter, I bet. Mark | |||||||||||||||||||
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Posted by Steve on May 21, 2008, 10:02 am
Please log in for more thread options
>
> > Hello all,
>
> > The differences between a parallelamplifierand abalancedamplifier
> > is rather confusing. Are they the same, or are they different? Both > > these circuits, and their advantages, appear to be very close to each > > other, if not the same... >
> > Just curious,
>
> > -Nick
>
> Parallel refers to the configuration of anamplifier'soutput circuit. > And now for something completely different. > > Balancedrefers to the nature of the either input or output > signals.Balancedmeans that the two lines of the output are referenced to > each > other and not to ground; the input's or load's voltage is measured > between two lines and voltages present on either line (as measured to > ground) are typically unintentional, undesired and are to be rejected > as extraneous. This is good for long runs, e.g. between a mic and an > amp input, because noise is mostly referenced to ground and is so > theoretically rejected. Whatever noise hits one line also hits the > other and so is ideally cancelled. > > Unbalanced signals are measured to ground, so are limited to short > runs where they won't be susceptible to noise pickup, e.g. between > adjacent audio components. (The run to a speaker is typically long, > but can get away with an unbalanced line by virture of a speaker's low > impedance, making it much, much less susceptible to noise. If someone > went crazy and designed a high-impedance speaker circuit, it would > benefit from abalancedoutput, too. Nobody's been that crazy yet.) > > As you might guess, a mic input, say, that is bothbalancedAND low > impedance, is the double-whammy for quietness. Professional mic inputs > are that way. Cheapo mic inputs are high-impedance and unbalanced, the > worst case, so they rely simply on short runs to avoid noise. If you > have to carry signals between two buildings that use separate ground > systems that may have a small difference between them (or a large one > if lightning or other surges strike!), then abalancedsystem would be > preferable so that the signals ignore the ground as much as possible. > Whole books are written on signals, grounding and noise reduction > tecniques. Many books. They come with magic wands. Thanks guys for the great input. The "parallel amplifiers" that I am speaking of are for HF PAs and LNAs, and are in parallel with each other and have Wilkinson dividers at their input and output. But the "balanced amplifiers" I have seen are also in parallel, but have a 90º hybrid power divider at their input and a 90º hybrid power combiner at their output. They look so darn close to each other, both circuit- wise and performance-wise, that it starts to get a bit confusing! Best, -Nick In this context, the balanced amp is usually used to cancel second order harmonics and second order intermod products. By careful matching of the phase shifts, you can get around 40 dB improvements in IP2, sometimes more, along with the 3 dB additional gain of the fundamental. Usually seen when the band is more than an octave wide, because second order intermods generated by 2 signals at the low end will be in-band near the top of the band. Steve | |||||||||||||||||||
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Posted by Nick on May 21, 2008, 12:06 pm
Please log in for more thread options >
> > > > > > > > > Hello all,
>
> > > The differences between a parallelamplifierand abalancedamplifier
> > > is rather confusing. Are they the same, or are they different? Both > > > these circuits, and their advantages, appear to be very close to each > > > other, if not the same... >
> > > Just curious,
>
> > > -Nick
>
> > Parallel refers to the configuration of anamplifier'soutput circuit.
> > And now for something completely different. >
> > Balancedrefers to the nature of the either input or output
> > signals.Balancedmeans that the two lines of the output are referenced to= > > each
> > other and not to ground; the input's or load's voltage is measured > > between two lines and voltages present on either line (as measured to > > ground) are typically unintentional, undesired and are to be rejected > > as extraneous. This is good for long runs, e.g. between a mic and an > > amp input, because noise is mostly referenced to ground and is so > > theoretically rejected. Whatever noise hits one line also hits the > > other and so is ideally cancelled. >
> > Unbalanced signals are measured to ground, so are limited to short
> > runs where they won't be susceptible to noise pickup, e.g. between > > adjacent audio components. (The run to a speaker is typically long, > > but can get away with an unbalanced line by virture of a speaker's low > > impedance, making it much, much less susceptible to noise. If someone > > went crazy and designed a high-impedance speaker circuit, it would > > benefit from abalancedoutput, too. Nobody's been that crazy yet.) >
> > As you might guess, a mic input, say, that is bothbalancedAND low
> > impedance, is the double-whammy for quietness. Professional mic inputs > > are that way. Cheapo mic inputs are high-impedance and unbalanced, the > > worst case, so they rely simply on short runs to avoid noise. If you > > have to carry signals between two buildings that use separate ground > > systems that may have a small difference between them (or a large one > > if lightning or other surges strike!), then abalancedsystem would be > > preferable so that the signals ignore the ground as much as possible. > > Whole books are written on signals, grounding and noise reduction > > tecniques. Many books. They come with magic wands. >
,
> =A0 Thanks guys for the great input. =A0The "parallel amplifiers" that I > am speaking of are for HF PAs and LNAs, and are in parallel with each > other and have Wilkinson dividers at their input and output. =A0But the > "balanced amplifiers" I have seen are also in parallel, but have a 90=BA > hybrid power divider at their input and a 90=BA hybrid power combiner at > their output. =A0They look so darn close to each other, both circuit- > wise and performance-wise, that it starts to get a bit confusing! > > Best, > > -Nick > > In this context, the balanced amp is usually used to cancel second order > harmonics and second order intermod products. By careful matching of the > phase shifts, you can get around 40 dB improvements in IP2, sometimes more= > along with the 3 dB additional gain of the fundamental. Usually seen when
> the band is more than an octave wide, because second order intermods > generated by 2 signals at the low end will be in-band near the top of the > band. > > Steve- Hide quoted text - > > - Show quoted text - Thanks for all the clarifying answers guys. Now it's finally clear! (Frank, linearity is not an issue for me, since I was just trying to fill in one of the many gaps in my electronics knowledge, and not actually trying to build either a parallel or balanced amplifier). Best regards, -Nick | |||||||||||||||||||
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