Design a Function Generator

[mona22]

Hi
I am going to design a function generator but i am in trouble at first step that is rectangular wave.
I tried to make it by op amp in astable mode but it must be work at 1MHZ and op amp is not a good way to design.
guys please help me to pass through my first step

that is to say that this generator must provide 1.5A in out put and the amplitude is 20V (peak-peak)
thanks

 

[AnalogKid]

1. It is bad form to hiack a thread with a different question. You should start your own thread.

2. You need a function generator that makes 1 MHz square wave, 20 Vpp, at 1.5 A? WHY???

ak

 

[mona22]

1. It is bad form to hiack a thread with a different question. You should start your own thread.

2. You need a function generator that makes 1 MHz square wave, 20 Vpp, at 1.5 A? WHY???

ak

I see that it is a bit confusing that why we need 1.5A and 1MHZ but it's a university project .

 

[AnalogKid]

Designing in a vacuum is not efficient. A university project to do what?

ak

 

[ronsimpson]

Hi
.......rectangular wave.
......1MHZ .
......must provide 1.5A in out put and the amplitude is 20V (peak-peak)

This output:
Will it only output "rectangular"? If you mix sign and rectangular then you need a different output amplifier.
20Vp-p, 10Vpk so you will need a +/- 15V supply if you are using a linear amp. 15V x 1.5A = 22.5 watts.
1Mhz? Will it output only 1Mhz or 0 to 1Mhz?
In rectangular mode, what rise and fall time? How fast must the edges be. -10V to +10V in 100nS?
What out put voltage? +/- 10V fixed or (o to 10V)

 

[mona22]

Designing in a vacuum is not efficient. A university project to do what?

ak

it has 3 marks of my final mark .
but the deadline was expired and i am trying to make it for my self

 

[mona22]

This output:
Will it only output "rectangular"? If you mix sign and rectangular then you need a different output amplifier.
20Vp-p, 10Vpk so you will need a +/- 15V supply if you are using a linear amp. 15V x 1.5A = 22.5 watts.
1Mhz? Will it output only 1Mhz or 0 to 1Mhz?
In rectangular mode, what rise and fall time? How fast must the edges be. -10V to +10V in 100nS?
What out put voltage? +/- 10V fixed or (o to 10V)

it must be contains three state of wave (rectangular-triangular-sin) these states of wave are in different out put voltage (yes they need different amplifier).
the out put frequency must be close to 1MHZ but not exactly constant, it should change in a few range of frequency. ex 800HZ-1.2MHZ .
the rise time is not important in this project but it should be a little.
about out put voltage : this is constant on 20 Vpp (-20V ===>> +20V) means : ((+20-(-20))= 40V

Now i have problem with choosing the way of making rectangular wave (making with op-amp has a limitation that op-amp is good to make frequency up to 10KHZ.)
(making with 555 has the same limitation because we need more that 1MHZ frequency )
Do know how i can make it with transistor in state of astable .???!!!

 

[ronsimpson]

Here is what I would do (step one)
Get the data sheet for the LTC6900. It is a good resistance to frequency oscillator.
You will need a good source of 5 volts or 3.3 volts. (LM7805)
R1 needs to be a fixed resistor and a pot. (you can do that)
The output is o to 5 volts, but I (you) can fix that later.
One IC, very small.

If I built this I would put a three way switch on "DIV" pin, and make a 1khz to 1mhz project. It would be much more useful.

 

[atferrari]

Good tho find someone as you who knew such a chip, Ron!

 

[ronsimpson]

If I was building for myself;
I would add a "buffer" IC. or an inverter. Between the LTC6900 and the output. Some IC that is in a socket that can be replaced easy.
I would not do 1.5A or +/-20 volts. I want a "TTL" logic level output. It is more useful.
You can get 1khz to 10mhz if you want.
Power from a cell phone charger or 9V battery.

I made many little projects like this.

 

[mona22]

Here is what I would do (step one)
Get the data sheet for the LTC6900. It is a good resistance to frequency oscillator.
You will need a good source of 5 volts or 3.3 volts. (LM7805)
R1 needs to be a fixed resistor and a pot. (you can do that)
The output is o to 5 volts, but I (you) can fix that later.
One IC, very small.
View attachment 96533
If I built this I would put a three way switch on "DIV" pin, and make a 1khz to 1mhz project. It would be much more useful.

You have a good memory to keep ICs
what simulator you used to test it?
this has the 0 to 5 volts output because of 5volt source , if i wanna improve it to +/-20 volts , I must change the source?am i right?
of course UR right about current and the output voltage but you know it's a uni project but i will change it to a complete thing that would be useful.

 

[ronsimpson]

The LCT6900 works from 3V to 5V only.
To get a different output I would make a amplifier. What output do you think is good for you? There are many applications for 3V and 5V and some for +/-1V for audio. I think +/-5V is good. Maybe +/-10V. (no 1.5A)
I use LTSpice. It is free. From linear.com It is built to work with their parts but will work with other parts.
Very common on this forum. Ask for help.

 

[mona22]

the circuit that you made was completely helpful for me and for having 1.5A I would add a darlington pair to amplify current. and for amplifying voltage i would add an op-amp but do you know what op-amp can work with 1.2 frequency?

 

[schmitt trigger]

An opamp which can amplify a 1.2 Mhz squarewave?

Assuming a +/-20 volt swing, and assuming that your required rise/fall times to be no larger than 5% of the total period, then you would require a slew rate of about 960 Volt/microsecond.
This is CRT-driver, video amplifier territory.