I am attempting to get the gain at or above 2. The first stage inverts the output with a gain of about 9, which is what I want. When I combine the stages, I am receiving a gain of about 0.35.
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1\$\begingroup\$ Click on Q2 collector and base to see if Q2 is saturated. According to my simple calculation, it is. \$\endgroup\$Willis Lin– Willis Lin2023-04-26 17:46:59 +00:00Commented Apr 26, 2023 at 17:46
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3 Answers
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Without doing any calculations, it looks to me like Q2 will be saturated so there's no Vce to work with. Adjust the DC bias appropriately to get some substantial Vce on Q2.
The Q2 base bias resistors may be a bit on the low side too, so they load the output of Q1 quite a bit (3KΩ||1.5kΩ = 1kΩ) .
answered Apr 26, 2023 at 17:39
Spehro 'speff' Pefhany
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\$\begingroup\$ So you'd suggest changing the base resistors for Q2? Is there any R value you think I should shoot for? Thanks in advance. \$\endgroup\$ChiefnBigNuts– ChiefnBigNuts2023-04-26 17:44:00 +00:00Commented Apr 26, 2023 at 17:44
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\$\begingroup\$ Q2 collector bias current is determined by the ratio of base resistors, Vbe, power supply voltage and Re3. Vce is V2- (IeRe3+ IcRc2) ~= V2-Ic*(Re3+Rc2). Depending on what you are trying to achieve for output swing and output Z you might have to adjust several resistors, but Re3 would be a place to start. \$\endgroup\$Spehro 'speff' Pefhany– Spehro 'speff' Pefhany2023-04-26 17:51:24 +00:00Commented Apr 26, 2023 at 17:51
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\$\begingroup\$ Increasing the values for the base bias resistors for Q2 resulted in an improved waveform, however, the output is distorted. Ideally I'd like to keep Re3 set to 50, as I am aiming for a 50 ohm impedance. \$\endgroup\$ChiefnBigNuts– ChiefnBigNuts2023-04-26 17:56:05 +00:00Commented Apr 26, 2023 at 17:56
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\$\begingroup\$ If you want Re3 to be 50 and you're happy with the base bias voltage then you have to decrease Rc2 so more of the voltage is dropped across the transistor. \$\endgroup\$Spehro 'speff' Pefhany– Spehro 'speff' Pefhany2023-04-26 18:00:17 +00:00Commented Apr 26, 2023 at 18:00
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I simulated your transistors separately with DC voltages.
The first transistor is good but the second transistor is biased wrongly then it is severely saturated. I fixed the biasing.
I used real transistors with part numbers and your microwave frequency is too high for them reducing the output level.
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The 0.5GHz microwave input frequency is so high that the saturated transistor cannot produce much fundamental frequency output level and absolutely not produce any of its severe distortion harmonics. Here is the output waveform at 100kHz which is where the transistor works properly:
