Push-Pull cross-over distortion ?

[Hammy]

Is it possible to reduce crossover distortion on a push-pull buffer in
a package where the bases are tied internally?

The package I'm talking about is here

http://i44.tinypic.com/2rhxo2q.png

The input signal is low Hz to 10MHz sine wave from a THS4222. I'm
after an output of 10Vpp into 50 ohm.

I can't use diodes like you typically would because of the way the
package ties the bases.

Typical diode compensated Push-Pull.

http://i41.tinypic.com/dh8uo7.png

I'm just wondering if anyone knows of any tricks.

I know I could use other BJT's but these are pretty nice single digit
nano-second rise/fall and storage times,high gain low Vce sat.


http://www.nxp.com/acrobat/datasheets/PMD3001D_1.pdf

 

[Hammy]

Depends on how you drive it.
Sometimes you can just put a resistor from the bases to the emittors,
at low signal levels (where the transistors are still off)
the driver then drives the load via the resistor.

+
|
c
---b
| e
----- drive ---------- R1-|
| |---------- out
| e
--b
c
|
-

Thank you Jan. I'll try that.

 

[Hammy]

Can you stand the dissipation if you class-A biased the output by
pulling a DC load current?

I used to do LM324's that way, so they could be used in active
filters.

...Jim Thompson

I'm trying to keep the power consumption to a minimum both to minimize
heat and to keep the power supply small. I'd like to get as wide a
swing (as close to +/- 5V) from a +/- 6V rails or less.

The THS422 can accept 15V max but the lower the rail voltage the less
dissipation in the output transistors. The less current the THS422
sinks/sources the wider the swing for the push/pull input which is why
I was looking at the dual NPN/PNP high gain low Vce sat duals.

This is for the output of a AD9834 10MHz signal generator I built a
while ago. Its only using a AD8057 to bump the filtered output up to
about 2Vpp. I'm considering ways to get this upto 10Vpp into 50 ohms
which seems to be the standard max output on most of the commercial
ones I looked at. I plan on using the THS422 as an adjustable gain
stage so I can have some amplitude adjustment. I haven't got that far
yet though ;-).

 

[Hammy]

Bridge feed forward compensation:

http://www.abvolt.com/misc/feedfwdbridge.jpg

If the bridge is balanced (R1 x R2 x C = L), then the compensation is
perfect.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

Thanks

I'll try that as well.

 

[Paul Keinanen]

Bridge feed forward compensation:

http://www.abvolt.com/misc/feedfwdbridge.jpg

If the bridge is balanced (R1 x R2 x C = L), then the compensation is
perfect.

Looks quite similar to the "current dumping" feed forward system used
in the Quad 405 power amplifier a few decades ago.

When the Quod 405 was introduced, there was a lot of discussion about
this kind of topologies for instance in Wireless World. This might
help googling for similar systems.