A BJT has hie = 6 kΩ and hfe = 224 at IC = 1 mA, with fT = 80 MHz and Cb'c = 12 pF. Determine (a) gm (b)rb'e (c) rbb' and (d) cb'e at room temperature and a collector current of 1 mA. Determine the parameters, gm, rb'e rbb' and Cb'e of the small signal high frequency model of the BJT.

Question

A BJT has [latex]h_{ie}[/latex] = 6 kΩ and [latex]h_{fe}[/latex] = 224 at [latex]I_{C}[/latex] = 1 mA, with [latex]f_{T}[/latex] = 80 MHz and [latex]C_{b^{'}c }[/latex]= 12 pF. Determine (a) [latex]g_{m} (b)r_{b^{'}e} (c) r_{bb^{'}} and (d) c_{b^{'}e}[/latex] at room temperature and a collector current of 1 mA. Determine the parameters, [latex]g_{m}, r_{b^{'}e} r_{bb^{'}} and C_{b^{'}e}[/latex] of the small signal high frequency model of the BJT.

Accepted Answer

[latex]g_{m}=\frac{I_{C}(mA)}{26 mV}=\frac{1}{26}=38.46 m mho[/latex]

[latex]r_{b^{'}e}=\frac{h_{fe}}{g_{m}}=\frac{224}{38.46 imes 10^{-3}}=5.824 k \Omega [/latex]

[latex]r_{bb^{'}}= h_{ie} – r_{b^{'}e} = 6000 – 5824 = 176 \Omega[/latex]

[latex]C_{b^{'}e}=\frac{g_{m}}{2\pi f_{T}}-C_{b^{'}c}[/latex]

[latex]=\frac{38.46 imes 10^{-3}}{2\pi imes 8 imes 10^{6} }-12 imes 10^{-12}[/latex]

[latex]= 76.5 × 10 ^{– 12} – 12 × 10^{ – 12} = 64.5 pF[/latex]

Question 11.10: A BJT has hie = 6 kΩ and hfe = 224 at IC = 1 mA, with fT = 8...

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