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For the following common-emitter amplifier, the original \$R_L = 4.7\space kΩ\$. When I replace it with a small value resistor (\$100\spaceΩ\$), the voltage gain will drop. Is there any way to drive the new low-impedance load without causing the degradation in the voltage gain?


Circuit Diagram

Circuit Diagram


SetUp Details

\$ \space \space \space \space \space \space \space \space R_G=600\space Ω \\ \space \space \space \space \space \space \space \space R_1=82\space kΩ \\ \space \space \space \space \space \space \space \space R_2=15\space kΩ \\ \space \space \space \space \space \space \space \space R_C=4.7\space kΩ\\ \space \space \space \space \space \space \space \space R_E=910\space Ω \\ \space \space \space \space \space \space \space \space R_L=4.7\space kΩ \$


Thank you for your help.

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  • \$\begingroup\$ Recalculate and redesign for the new operating point with the new load. \$\endgroup\$ – Eugene Sh. Feb 25 '15 at 18:09
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    \$\begingroup\$ Or add a buffer stage to the output. \$\endgroup\$ – The Photon Feb 25 '15 at 18:13
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    \$\begingroup\$ Add an emitter follower (comon collector) or a full push pull stage. \$\endgroup\$ – jippie Feb 25 '15 at 18:21
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Your output resistance is mostly controlled by Rc, which is 4.7k, so you are going to get a lot of loss driving such a small load resistance. To maintain gain and drive the low resistance you need a common collector buffer, as Photon said.

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  • \$\begingroup\$ How to integrate the common-collector buffer into the circuit? Thank you. \$\endgroup\$ – Casper Feb 25 '15 at 18:31

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