high voltage amplifier with wide frequency range

[Helmut Sennewald]

Hi,

I have to design a high voltage amplifier, that should amplifiy a 3Vpp
sinussodial signal up to 300Vpp. Furthermore the amplifier should work
with linear phase over the whole frequency range from 100kHz to 4 MHz.
The load of the amplifier will be a capacitance from 2pF and a
resistor with changing values higher than 100MOhm. The current, the
amplifier should provide, is only up to 500mA. I need this amplifier
for a measurement application.

I tried in the last days a cascode amplifier which was able to amplify
the sinussodial up to 300Vpp. The great Problem is, that the sinus
will be deformed. Additionally the phase isn't linear over the
interesting frequency range. I also tried a complentary booster, but
this couldn't provide the high voltage.

Is there anybody, who can help me?

Thanks for your help,
Steff

Hello Steff,

Apex Microtech makes high voltage amplifiers.
http://apex.cirrus.com/en/products/apex/index.html
Distributor in Germany is Hy-Line.
http://www.hy-line.de/
I think even the fastest of their amps is too slow for your application.
Required slewrate:
150V*2*pi*4e6 = 3800V/us

Last but not least, if you have a cable at the amp-output,
it will have at least 0.5pF/cm. The 2pF load you have in mind
is nothing compared to the capacitance of a possible cable.

Best regards,
Helmut from Germany

 

[[email protected]]

Hi,

I have to design a high voltage amplifier, that should amplifiy a 3Vpp
sinussodial signal up to 300Vpp. Furthermore the amplifier should work
with linear phase over the whole frequency range from 100kHz to 4 MHz.
The load of the amplifier will be a capacitance from 2pF and a
resistor with changing values higher than 100MOhm. The current, the
amplifier should provide, is only up to 500mA. I need this amplifier
for a measurement application.

I tried in the last days a cascode amplifier which was able to amplify
the sinussodial up to 300Vpp. The great Problem is, that the sinus
will be deformed. Additionally the phase isn't linear over the
interesting frequency range. I also tried a complentary booster, but
this couldn't provide the high voltage.

Is there anybody, who can help me?

Thanks for your help,
Steff

 

[[email protected]]

.5A @ 300V is a lot of watts, are you sure you mean 500 mA?
Anyways you never get 500 mA in 2 pF with 100 MOhm @ 4 MHz and 300 V

I think Winfield has published some related designs here in the past, google?

Sorry, there was a mistake from me. The maximum current I expect is
50mA.

 

[mike]

Try your luck at Apex Microtechnology...
http://apex.cirrus.com/en/products/apex/matrix_all.html


D from BC
British Columbia
Canada

Sinusoids have only two parameters, amplitude and frequency.
Sometimes it's easier to generate them than to amplify them.
If your signal is a modulated sinusoid, you may find that you
need bandwidth in excess of the carrier frequency.

Look into some of the techniques being proposed for cellular
base station amplifiers to achieve high linearity with
efficiencies higher than what's obtainable with Class A.

 

[Helmut Sennewald]

Hello Steff,

Apex Microtech makes high voltage amplifiers.
http://apex.cirrus.com/en/products/apex/index.html
Distributor in Germany is Hy-Line.
http://www.hy-line.de/
I think even the fastest of their amps is too slow for your application.
Required slewrate:
150V*2*pi*4e6 = 3800V/us

Last but not least, if you have a cable at the amp-output,
it will have at least 0.5pF/cm. The 2pF load you have in mind
is nothing compared to the capacitance of a possible cable.

Best regards,
Helmut from Germany

Hello Steffen,
just one more idea to reduce the high voltage requirement
for the transistors. Try to use a good transformer.
Therefore you should look in the RF-handbooks for wide
bandwidth power amplifiers.

Best regards,
Helmut

 

[Paul]

Hi,

I have to design a high voltage amplifier, that should amplifiy a 3Vpp
sinussodial signal up to 300Vpp. Furthermore the amplifier should work
with linear phase over the whole frequency range from 100kHz to 4 MHz.
The load of the amplifier will be a capacitance from 2pF and a
resistor with changing values higher than 100MOhm. The current, the
amplifier should provide, is only up to 500mA. I need this amplifier
for a measurement application.

I tried in the last days a cascode amplifier which was able to amplify
the sinussodial up to 300Vpp. The great Problem is, that the sinus
will be deformed. Additionally the phase isn't linear over the
interesting frequency range. I also tried a complentary booster, but
this couldn't provide the high voltage.

What do you mean by "linear phase"? Are you specifying a
maximum phase shift over your frequency range, or are you asking for a
specific type of filter response and group delay response?
If you want very little phase shift, you may be asking for
considerable current drive. For a 5 degree phase shift, your amplifer
effective output impedance needs to be between 1500 & 2000 ohms.
That means you need to be able to drive betwwen 150-200 mA at 4 MHz.
Maybe the 500 mA requirement wasn't as silly as first sounded.
To be able to keep the amp from slew rate limitation, you need
about 8-10 mA, but at that limit, your phase shift will be pretty bad.
The 19Kohm reactance fo the 2pf at 4MHz means that a source impedance
of 19K will cause a 45 degree phase shift, and a -3db drop in signal
amplitude. Is that within you requirements?
Since you are making measurements, you should tell us what the
accuracy is in terms of amplitude, phase shift, and linearity. If the
wave form you're measuring is sinusoidal, these are all you might
need. For complex waveforms, more requirements would have to be
specified (ie., group delay, overshoot, etc.).

-Paul