Base Bias Constant Voltage Source
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Posted by dgc on January 10, 2006, 7:00 am
Please log in for more thread options As a result of a reference I saw in a reply to one of my earlier posts, I bought the book "Radio Frequency Transistors" by Dye and Granberg. At the bottom of page 61 they say " ... the base bias supply must be able to supply current without considerable excursion in the base-emitter voltage between the no signal and the maximum signal conditions. This requires a constant voltage source, as variations of a few millivolts represent a large portion of the nominal 0.63-0.67 volt typical value." My question is; how can a variation of a few millivolts have an appreciable impact on the base-emitter voltage when the bias can be set at 2,3,4 or more volts to begin with? I t would seem to be negligible in terms of the amount of main bias voltage present on the base. Second question: Exactly how can the low voltage signal (say 100 milivolts peak) affecting the bias in any significant way to begin with? Third question: What impact is all this having on a common emitter circuit set up for linear amplification? Any help in understanding this will be much appreciated. | ||||||||||||||||||||||||||||||||||||||||
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Posted by Jon on January 10, 2006, 6:18 am
Please log in for more thread options It's difficult to answer your questions without seeing the circuit. Your first question makes reference to the bias voltage of 2, 3, 4 volts. Regardless of the bias circuit, the base emitter voltage is a function of the base-emitter diode characteristic, and will be on the order of .65V. Can you supply a circuit? Regards, Jon | ||||||||||||||||||||||||||||||||||||||||
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Posted by Jim Thompson on January 10, 2006, 8:05 am
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wrote: Sounds like BS from someone who learned tooobz, and could then never figure out transistors. [snip] ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. | ||||||||||||||||||||||||||||||||||||||||
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Posted by Robert Baer on January 11, 2006, 9:10 am
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Jim Thompson wrote: > wrote:
> > >>As a result of a reference I saw in a reply to one of my earlier posts, I
>>bought the book "Radio Frequency Transistors" by Dye and Granberg. At the >>bottom of page 61 they say " ... the base bias supply must be able to supply >>current without considerable excursion in the base-emitter voltage between >>the no signal and the maximum signal conditions. This requires a constant >>voltage source, as variations of a few millivolts represent a large portion >>of the nominal 0.63-0.67 volt typical value." >
Refer them back to Shakespere: To Be or not Toobee...
> > Sounds like BS from someone who learned tooobz, and could then never > figure out transistors. > > [snip] > > ...Jim Thompson | ||||||||||||||||||||||||||||||||||||||||
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Posted by Winfield Hill on January 11, 2006, 2:43 am
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Robert Baer wrote... >
> Refer them back to Shakespere: To Be or not Toobee... Groan... Was that necessary? -- Thanks, - Win | ||||||||||||||||||||||||||||||||||||||||
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>bought the book "Radio Frequency Transistors" by Dye and Granberg. At the
>bottom of page 61 they say " ... the base bias supply must be able to supply
>current without considerable excursion in the base-emitter voltage between
>the no signal and the maximum signal conditions. This requires a constant
>voltage source, as variations of a few millivolts represent a large portion
>of the nominal 0.63-0.67 volt typical value."