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Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
References: <3DF6537E.B0FC9DBE@worldonline.fr> <3DF90203.C9691374@worldonline.fr> <3DF98E5B.D86102A5@worldonline.fr>
Subject: Re: Determining bjt noise parameters for Spice models?
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Date: Fri, 13 Dec 2002 09:21:57 -0000
NNTP-Posting-Date: Fri, 13 Dec 2002 09:22:01 GMT
> Kevin Aylward wrote:
>> A.Iakovlev wrote:
>>> Kevin, Thank you.
>>> Kevin Aylward wrote:
>>>> Just about. You need to make sure the base resistance is set right.
>>>> This is the main variable that distinguishes transistor noise form
>>>> exh other. Other noise contributions are inherently fixed by Ic and
>>>> hfe. So, after the 1/f curve flattens out, set rbb until the flat
>>>> portion reads correctly. Do this at a highish collector current,
>>>> e.g 10ma, also with r source set to zero.
>>> I've tried to do this at 10kHz in the following way:
>> KF needs to be set at a low frequency, say 10 Hz.
> I've started with the thermal noise, estimating that the flicker noise
> vanishes at 10kHz. Was it a wrong approach?
That's ok for rbb noise and shot noise. I as stating that you cannot
determine the 1/f co-efficient at high frequencies.
>>> - common emitter;
>>> - collector connected to a voltage source in series with a
>>> - base directly connected to a voltage source (VSRC, small AC);
>>> - the base voltage source adjusted to get about 10mA collector
>>> - equivalent input noise calculated as V(ONOISE) on the collector
>>> divided by the gain calculated (by Spice)
>>> on the input AC.
>>> Doing that with the standard 2SC3329 model and varying RB from 2 to
>>> 10 Ohm could not reach the 0.6nV/rtHz specified by the datasheet -
>>> much lower levels obtained; the datasheet announces rb about 2Ohm.
>> I dont understand whatvyou say here. Is the spice value too high or
>> too low?
> Sorry. The value calculated (not directly by Spice but by me, from
> the V(ONOISE) provided by Spice) was much lower than 0.6 nV/rtHz.
At 290 deg, 20 ohms gives 0.57 nv/rthz. At 10ma the collector noise =
0.141 nv, which is getting close to 0.6nv when you sum the squares.
What does the spice V(INOISE) give?
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
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