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Fet bjt vs fet bjt current controlled device current

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Unformatted text preview: rking Transistor EE 332 Spring 2013 BJT vs. FET BJT vs. FET • BJT : Current Controlled Device – Current Amplification – Constant Current Source Small input current controls large output current • FET : Voltage Controlled Device – Switch “on” and “off” – Digital Circuit Small input voltage controls output current EE 332 Spring 2013 B Junction Transistors Bipolar ipolar Junction Transistors EE 332 Spring 2013 Note, BJT = current-controlled current switch = always have some current flowing = power dissipation This is its Achilles’ heel compared to the MOSFET, more power dissipation limits integration level per chip. Charge Transport Charge Transport in BJT in BJT BJTs have been gradually replaced with CMOS especially in high-density logic apps over past 30 yrs. But, BJTs are better for analog circuit applications higher speed and gain. Remember the P-N diode with the lights turned on! EE 332 Spring 2013 Operation of BJT EE 332 Spring 2013 Fusing Terminals of Two PN Junctions P N si W + - Vappl > 0 P N W+ - Vappl < 0 Holes from P region (“Emitter”) of 1st PN junction driven by FB of 1st PN junction into central N region (“Base”) Driven by RB of 2nd PN junction from Base into P region of 2nd junction (“Collector”) •  1st region forward bias, 2nd reverse bias •  If we want to worry about holes alone, need P+ on 1st region •  For holes to be removed by collector, base region must be thin EE 332 Spring 2013 Draw like Streetman...
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