Electronics 2 Test 3
what is the usual value fo Vbe?
The dc analysis of transistor circuits is greatly simplified by assuming that VBE = 0.7 V. Refer to Table 6.3.
model parameters for small signal models (re?)
Va = 1/lamda and only occurs for modulation? re = 1/gm = alpha /gm if alpha is nearly 1
what is base width modulation?
Vce increases, increasing ic
What do you need to remember about summing certain voltage markers with sources under them?
Vs -Ic Rc = Vc -Vs+ ReIE = VE
what is a BJT current source? what is the relation between reference and output current?
can be 2vcc-vbe in case of connecting bottom transistor to negative version of vcc
how to derive common emitter output resistance, input resistance, and gain?
dependent source open circuits when you apply source voltage in parallel
What is the typical VCE voltage in saturation vs edge of saturation? REVIEW
for pnp, it is VEC
npn vs pnp circuit smybols and polarities in active mode as well as each current what about their base vs emitter voltage?
ic + ib = iE npn = +VBE pnp = +VEB = - VBE
Summary of equations to be known for BJTs in when do these equations apply? REVIEW!!!
ic +ib = iE ic = collector current/ib = base current/ ie = emitter current Is = saturation current = 10^-12 to 10^-18 = scale current Vt = .0259 V B = common emittter current gain (large 50-1000) Alpha = common base current gain (small <1) applies in active mode and edge of saturation
what are the models for small signal bjts?
ic = gm vpi vpi = vbe ib = vpie/rpie
classical bjt amplifier model and what to remember - where do load resistances run, REVIEW
if the rsignal is not 0, vpie != Vsignal, so you will need to solve for vpie// vpie is only over the resistance rpie
how do you deal with multistage amplifiers?
multiply togehter their individual gains to find total overall gain A1*A2...An
how do you deal with parallel load BJTs?
notes
vbe on pnp vs npn transistor
npn vbe = .7 pnp veb = .7
amplifier models for bjts
output over RC unless common collector common base has AC input on emitter side
how to derive the current in small signal BJT?
re=Vt/Ie
easiest way to relate current and resistance of small signals?
rpi =(B+1)re rpie = Vt/Ib
how do you separate differntial amplifier which uses a common node techniques?
separate so 2 reistances on each side treat as common emitter with Re to find the gain
what are the two types of BJTs, what are the contacts on each, and what are the two junctions?
VBE = EBJ VCB = CBJ collector, base, emiiter
which models do you use for CS and CE, CG and CB, CD and CC?
CS and CE - pi model, ground on bottom CG and CB - ground on gate left side, use both XS amplifier - use both
How do we expect a capacitor to act for amplifiers?
Coupling capacitor in the range of 1uf to 100uF DC = CC is open circuit low freuqnecy = OC midband = shortcircuit high frequency = ?
what is the load line for a BJT? what is the operating point?
Qpoint = (Icq, VCE) you are looking for a point in active mode!
BJT modes of operation REVIEW
To ensure operation in the active mode, the collector voltage of an npn transistor must be kept higher than approximately 0.4 V below the base voltage. For a pnp transistor, the collector voltage must be lower than approximately 0.4 V above the base voltage. Otherwise, the CBJ becomes forward biased, and the transistor enters the saturation region. when assuming active mode - usually assume because this amplification VEB >0 (forward) VBC<=0 (reverse)
how do you solve small signal equivelants?
this basically puts all resistances on the drain side in parallel since they are all gonna be with respect to ground once you turn off all DC source voltage source = short circuits current sources = open circuits?
how to solve for small signal gain in a BJT differential amplifier? WHAT TO NOTE?
this can change depending on the resistance put on the model
Current flow in an npn transistor biased to operate in the active mode. (Reverse current components due to drift of thermally generated minority carriers are not shown.)
this causes current to flow away from the collector which means electrons flow to it
how do you derive common collector?, or emitter follower
use T model, other you can use Pi model then just use voltage division
what is the gain?
vo/vin
small signal differential amplifier BJT gain when RE =0 and doesnt equal 0
when =0 it is gmRc
what is the forced Beta and when is it used? REVIEW?
when operating in saturation, old equations are dismissed (ones involving B and Alpha), but the equation ib+ic=ie always holds assume VCE = .2 V not used for edge of saturation, only for deep saturation
