Synchronized Sweep Generator

[Eshal]

Here is my page from the lab manual. We have industrial electronics in this semester and we have given with this lab manual (page is shown below). I didn't include the Table 4.1 and Table 4.2 as said in the page.



OK, so come the point.
We didn't study yet what is synchronized sweep generator. The fact is, our lab is going a head of the class. That's why we didn't study this circuit in the class too. I am not getting what is this. We didn't learn this before in any semester. I want to understand its working that how it is producing output from taking input. I want to learn its purpose. I want to know what does it do and why we need it and where we need it. Its application. In short, I want to know it all but briefly.

Thank you sir.

 

[betwixt]

Re: Synchronized sweep generator

It's simply a voltage ramp generator with a trigger to start the ramp climbing. The bipolar transistor is configured as a constant current generator so the voltage across the capacitor rises linearly. The unijunction is the trigger to discharge it and is itself triggered by the incoming signal (which although unmarked is point 'A' in the schematic).

These sorts of circuits are used when something controlled by a voltage has to be synchronized to a trigger. For example, if you were testing a filter bandwidth you would use the voltage to sweep an oscillator across the desired filter range and trigger a measurement device (perhaps an oscilloscope) at the start of the sweep. It would then draw the frequency/amplitude graph of the filter characteristic. For more on this I suggest you look up "spectum analyzer" and "tracking generator".

It can also be used in the amplitude domain, for example it you connected the output voltage to an amplifier and monitored the input against output on an X-Y display it would demonstrate the amplifiers linearity.

These days, this kind of circuit is more often replaced by digital ramp generators (increasing count fed to a DAC) because they are not dependant on setting the constant current generator for each capacitor value.

Brian.

 

[Eshal]

Re: Synchronized sweep generator

(which although unmarked is point 'A' in the schematic).

Ohhh sorry, Point A is a input. Yes, you guessed it right.

And what does Zener and diode are doing here? Why one is zener and other is simple diode. Why not both are diodes?

These sorts of circuits are used when something controlled by a voltage has to be synchronized to a trigger. For example, if you were testing a filter bandwidth you would use the voltage to sweep an oscillator across the desired filter range and trigger a measurement device (perhaps an oscilloscope) at the start of the sweep. It would then draw the frequency/amplitude graph of the filter characteristic.

Sorry sir, I didn't get it. Actually this is very new to me. So I think it will take time to make me learn this.

For more on this I suggest you look up "spectum analyzer" and "tracking generator".

Are these both related to my topic the "synchronized sweep generator"?

It can also be used in the amplitude domain, for example it you connected the output voltage to an amplifier and monitored the input against output on an X-Y display it would demonstrate the amplifiers linearity.

Understood sir.

These days, this kind of circuit is more often replaced by digital ramp generators (increasing count fed to a DAC) because they are not dependant on setting the constant current generator for each capacitor value.

Ofcourse, many analog devices are being replaced with digital one. But analog are still basics so that's why they are still of great value to learn, I guess.

CONCLUSION:
Overall, very great explanation in a brief manner.

Would you like to recommend and any good Industrial Electronics Book which could include these circuits too and major topics?
I remember, you have helped me before on my posts.

Thank you very much.

 

[betwixt]

Re: Synchronized sweep generator

I will try to explain in more detail:

The zener diode and ordinary diode are (were - the image has disappeared!) to provide a constant voltage on the base of the transistor. The zener is used in reverse (breakdown) mode so it drops a stable voltage across it according to the type you use, the other diode is forward conducting and adds 0.6V (Vf) to it. With constant base voltage, the emitter voltage will also be constant (Vbe) so the current through the transistor is set by the potentiometer. In that configuration, the collector current will be constant so the charge current to the capacitor will also be constant and that produces a linear rather than exponential rise in voltage across it. When triggered by the signal, the unijuncton transistor discharges the capacitor so the voltage across it is almost zero, it then rises linearly up to the point where the circuit can no longer add charge to it. The result is a linear ramp voltage, starting when triggered, thats why it's called 'synchronized'.

The circuit is used widely in spectrum analysers and tracking generators, that's why I suggested looking at them. If nothing else they should explain the use of linear voltage ramps and how they are used to control oscillators.

I'm afraid I can't help with any books, all mine date back 40 years or more! They are a little out of date!

Brian.