High cut-off frequency in CE amplifier

[honest]

I have a CE amplifier.

With real instrumentation, real circuit I got a high cut-off frequency
of about 600 kHz while if I repeat it in PSpice I got about 200 MHz (!)

Same circuit with LT Spice I got about 3,5MHz

The device is 2N3904

I saw in an example provided by LTspice that there is a
100pF capacitor between C and B...

Pheraps Miller effect isn't calculated by Spice?

Thanks in advance.

 

[Jim Thompson]

On Sun, 25 Oct 2009 11:07:57 +0100, honest <none@host.com> wrote:

I have a CE amplifier.

With real instrumentation, real circuit I got a high cut-off frequency
of about 600 kHz while if I repeat it in PSpice I got about 200 MHz (!)

Same circuit with LT Spice I got about 3,5MHz

The device is 2N3904

I saw in an example provided by LTspice that there is a
100pF capacitor between C and B...

Pheraps Miller effect isn't calculated by Spice?

Thanks in advance.

Without a schematic we know nothing. And... What is your definition
of cut-off frequency?

...Jim Thompson
--
| James E.Thompson, CTO | mens |
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| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
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With Half My Brain Tied Behind My Back
Still More Clever Than Mr.Prissy Pants

 

[Jamie]

honest wrote:

I have a CE amplifier.

With real instrumentation, real circuit I got a high cut-off frequency
of about 600 kHz while if I repeat it in PSpice I got about 200 MHz (!)

Same circuit with LT Spice I got about 3,5MHz

The device is 2N3904

I saw in an example provided by LTspice that there is a
100pF capacitor between C and B...

Pheraps Miller effect isn't calculated by Spice?

Thanks in advance.
Maybe.

How this for a start.

1. Wrong board lay out. (Un calculated Capacitance &/ induction)

1A. Un expected LC taking place.

2. Wrong type of resistors.

3. Not putting a local bypass caps in.

4. Local bypass caps if #3 has been done, aren't using a non inductive
type.

5. Design has to high of R values, but Spice should of picked up on that.

6. Your transistor is a fake knock off or just something that was
around and stamped as so.


7. The simulator is just wrong! (no surprise there)

 

[honest]

Jamie ha scritto:

1. Wrong board lay out. (Un calculated Capacitance &/ induction)

This one. Found the issue.
Thanks again.