Biasing this FET -- how does the bias work??
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Posted by billcalley on June 27, 2006, 10:18 pm
Please log in for more thread options I know how to bias FETS, but how this particular Class A linear bias scheme works has me completely stumped, since the DC is totally blocked from the FET's gate by capacitors. Anyone have an explanation of the bias of this particular FET circuit? The small signal amplifier circuit can be seen at Watkin's Johnson Web site at: http://www.wj.com/documents/Datasheets/FH101.pdf . Any help in understanding this particular bias circuit would be most appreciated! Thanks, Bill | |||||||||||||||||||||||||||||||
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Posted by John Popelish on June 27, 2006, 10:33 pm
Please log in for more thread options billcalley wrote: In every schematic on that data sheet, it seems that there is a DC path to ground (either a resistor, an inductor, or a series combination). That means that the bias voltage is zero in all these cases. | |||||||||||||||||||||||||||||||
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Posted by billcalley on June 27, 2006, 10:38 pm
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Thanks John, but since the bias voltage is, as you say, zero volts at the gate, then how can it function as a Class A small signal linear amplifier? I would think it could only function as a Class C amp...? Thanks Again, Bill John Popelish wrote: > billcalley wrote:
> > I know how to bias FETS, but how this particular Class A linear
> > bias scheme works has me completely stumped, since the DC is totally > > blocked from the FET's gate by capacitors. Anyone have an explanation > > of the bias of this particular FET circuit? The small signal amplifier > > circuit can be seen at Watkin's Johnson Web site at: > > http://www.wj.com/documents/Datasheets/FH101.pdf . Any help in > > understanding this particular bias circuit would be most appreciated! >
> In every schematic on that data sheet, it seems that there is a DC > path to ground (either a resistor, an inductor, or a series > combination). That means that the bias voltage is zero in all these > cases. | |||||||||||||||||||||||||||||||
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Posted by Phil Allison on June 27, 2006, 10:44 pm
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"billcalley" >
> Thanks John, but since the bias voltage is, as you say, zero volts at > the gate, then how can it function as a Class A small signal linear > amplifier? ** WAKE UP !! It is NOT a mosfet !! The gate does not need to be biased for the device to conduct. ...... Phil | |||||||||||||||||||||||||||||||
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Posted by on June 28, 2006, 7:36 am
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Phil Allison wrote: > "billcalley"
> >
> > Thanks John, but since the bias voltage is, as you say, zero volts at > > the gate, then how can it function as a Class A small signal linear > > amplifier? >
> > ** WAKE UP !! > > It is NOT a mosfet !! > > The gate does not need to be biased for the device to conduct. Calm down Phil, this is electronics BASICS. >
> > > > > ...... Phil | |||||||||||||||||||||||||||||||
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> bias scheme works has me completely stumped, since the DC is totally
> blocked from the FET's gate by capacitors. Anyone have an explanation
> of the bias of this particular FET circuit? The small signal amplifier
> circuit can be seen at Watkin's Johnson Web site at:
> http://www.wj.com/documents/Datasheets/FH101.pdf . Any help in
> understanding this particular bias circuit would be most appreciated!