Amplitude Modulation Circuit

310

05:22:36

Voltage controlled variable gain amplifier. 

published 5 years ago

fatcat2

5 years ago

What purpose does that 1M ohm resistor serve?

hurz

5 years ago

everycircuit bjts are like perfect current soures. BJT have no early voltage and any very little change in Beta DC gain (e.g 100 top, 101 lower bjt) the operating point will run away. The Meg Ohm shall stablise this. But it shows the main problem of this topology/circuit

Sheen140

5 years ago

@hurz you're totally right, this circuit DOES NOT work in real life at all. To start you'd need perfectly matched transistors for the current mirrors, perfectly offset voltages on the phase splitter, and extremely low noise DC biasing voltages to get this to work. Plus my phase splitter BJT seemed to need a ridiculously high beta (1,000) to get this to work. Stick to gilbert cells folks!

fatcat2

5 years ago

What is the problem if EC doesn't stimulate early effect?

Sheen140

5 years ago

@fatcat2 Not exactly sure about the early effect issue, but the simulation assuming ideal transistors that are perfectly matched with fairly high current gain. I need to study more about the early effect again to be honest

hurz

5 years ago

the missing early effect, or better said its close to infinite high voltage makes BJT collectors almost infinite in its resistance and perfect as current source. So two collectors connected together are instable or better saud labile. Only very very little changes at on collector side and the operating point flips over. To stabilise it need some parasitic resistors, it will help to make it even work irl.

fatcat2

5 years ago

And that means EC doesn't follow any hybrid parameters...

fatcat2

5 years ago

@Sheen140, will this issue be eased out if we use a Wilson current mirror instead?

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.