Alright, here's what the circuit looks like now. The results are wrong though. I can't seem to get a 0.6V difference between the cathode and anode of the diode, perhaps because of the specific diode I'm using in the simulation. Also attached is the output graph. The negative side is partly...
Oh no problem, we all make mistakes. We wouldn't learn anything if we didn't.
That makes better sense. Right now it's cutoff around zero. The negative portion of the signal is cutoff.
Thanks,
Mike
Oh I know to use resistors to bias the diode. I just don't know where to connect the other end. I tried the connection shown in the attachment, which I know is wrong, since I'm getting the wrong output. I just realized that the diode is not forward biased in this circuit. Adding an Rc resistor...
I think I understand what you mean. I want to cancel out the -600.8mV by adding +600.8mV to that? I don't see how to hook up the other end of the diode to achieve that. I know you gave me a big clue. I'm also noticing that there's zero volts at the base of Q1.
Thanks,
Mike
Ok, there is a voltage drop of 4.4V across R3 leaving -600mV at the emitter. The negative supply confuses me. I haven't worked with any circuits like this involving a negative supply, just ground.
I have 1V for the base voltage minus the roughly 0.7V drop across Vbe. I know I need something...
I'm always open to other ideas.
I've got the basic emitter-follower down. The output is offset by about -600.8mV. There is not supposed to be any offset, but I'm not seeing how to get rid of it.
Thanks,
Mike
That's a great tip! The attachment shows an example and it looks like the input voltage is 0 to Vref. I'm not sure what the other two Vin's mean. The design parameters didn't include the input voltage range, just the maximum frequency, which is 100 kHz.
The emitter-follower I attached is good...
Well one problem is, I don't know what a typical analog input voltage looks like. Do they typically go below ground? What's the voltage swing?
Don't MOSFET's have higher input impedance and lower quiescent current than BJT's?
Thanks,
Mike
Found a 2N3906 and put that in the circuit, but now I'm getting a negative voltage at the gates of M3 and M4. I'm looking this problem wrong. What am I missing? How do I provide a negative voltage to the bottom while also providing the bias current? Is there a better bias current source I could...
The specifications for this project include the use of discrete parts and an input signal of up to 100 kHz. This is going to be an 8-bit converter. My instructor does allow the use of some non-discrete parts, I just have to ask him about them. I've chosen a 12 MHz clock and 1/8th of that is 1.5...
I like the seesaw analogy. I forgot to mention that I don't know how to choose the bias current value also. The 2N7000 in this circuit is a custom part and I'm not sure I attached the pin numbers to the right label (gate, drain, source). The data sheet doesn't say which number is which.
This...
I need to design a unity gain amplifier for a sample and hold circuit. I've decided to use the circuit shown in the attachment. Now I know the gain = 0.5(Gm2*R1)[(Gm3*R2)/(1 + Gm3*R2)]. The 2N7000 has a Gm of 0.1, so that gets me the values of R1 and R2. I don't know if these are good values to...
I can put multiple probes at the same time. I just forgot I could do that! lol
There's a voltage drop across M1 and M2, so the resistor has to overcome those drops to put enough voltage on the base of Q1. If I built this circuit as seen in my previous post, the current could rise considerably...
I'm planning to use a single M2 transistor for each LED. It seems to me that, since the supply voltage will be held constant via the voltage regulator, I won't need the constant current source and could just use a resistor. I'm not sure what you mean by multiple traces at one time.
I got the...
Actually, the maximum current for these LED's is 700mA. I'm just running them at the current they will naturally take for a given voltage. My goal is to flash 25 LED's one at a time so that only one is on at any time rather than all of them at the same time. It seems logical to me. The flashing...