phn10
Newbie level 4
Hi,
I'm reading a book about AM receiver radio. The author designed a 1.5V low power radio, which used a 2-stage common-emitter amplifier to get the gain of 200 (attached image as AM receiver radio.jpg). The author said 1 amplifier has limtied gain, and to get the 200 gain, he needed to use 2 amplifier stages. I don't understand this point.
Based on my knowledge, the gain of the common-emmiter amplifier is Rc/re, in which Rc is collector impedance, and re is base-emitter internal resistance. So based on this equation, given that the ciruit is biased correctly and Vce > Vce(sat), the gain of 1 amplfiier can definately go above 10, even hundreds or thousands. So instead of use 2 amplifiers, I can design a circuit with the same gain with only 1 amplifier.
Does anyone know what is wrong with my assumption?
Note: I also attach a LTspice simulation of my design (attached image as gain_200.png), the input voltage is 4mV, and output voltage is 800mV, so the simulative gain is 200. I built an actual circuit with the same components, but the gain is only 3!!??? Can anyone speculate what is wrong?
Thanks
I'm reading a book about AM receiver radio. The author designed a 1.5V low power radio, which used a 2-stage common-emitter amplifier to get the gain of 200 (attached image as AM receiver radio.jpg). The author said 1 amplifier has limtied gain, and to get the 200 gain, he needed to use 2 amplifier stages. I don't understand this point.
Based on my knowledge, the gain of the common-emmiter amplifier is Rc/re, in which Rc is collector impedance, and re is base-emitter internal resistance. So based on this equation, given that the ciruit is biased correctly and Vce > Vce(sat), the gain of 1 amplfiier can definately go above 10, even hundreds or thousands. So instead of use 2 amplifiers, I can design a circuit with the same gain with only 1 amplifier.
Does anyone know what is wrong with my assumption?
Note: I also attach a LTspice simulation of my design (attached image as gain_200.png), the input voltage is 4mV, and output voltage is 800mV, so the simulative gain is 200. I built an actual circuit with the same components, but the gain is only 3!!??? Can anyone speculate what is wrong?
Thanks