Function generator ICs

[Zero999]

W2AEW has an easy square/triangle wave-shaper circuit where you could add output filters to get a sine wave. I'm not sure about getting it to 300khz though.. If you need bi-polar, you can level-shift unipolar to bipolar on the output opamp.

Using a diode bridge to switch currents into a capacitor as W2AEW shows is one of the higher performance options and suitable for operation up to at least 40MHz so 300kHz is not a problem and it used to be the go-to function generator topology.  Using currents and an integration capacitor avoids bandwidth limitations of an operational integrator.  The low capacitance of the diodes lowers the amount of charge from switching coupled into the integration capacitor making compensation of this error more effective.  Both contribute to good control of the triangle wave height which is required for low distortion sine shaping.

Interesting. I've built the integrator triangle wave generator before and have found the the jellybean LM393 comparator's propagation delay seemed to be more of a limiting factor, than the integrator.

The main downside I can see with the current source/sink solution is, if 50% duty cycle is required, getting the currents to match accurately could be challenging.

[calexanian]

Jameco shows 1339 of them in stock. Interestingly enough I think that may be the last place i bought them in anger perhaps 15 years ago. I remember getting tubes from digikey and they were like .45 each. I also recall that many hundreds of thousands of them in SIOC were packaged and floating about out there when they were discontinued.

[nuno]

When I started exploring PSoC4 I played a bit with generating a triangle wave. Made a concept for an "analog" triangle wave generator without any CPU intervention, and didn't develop the thing further. TimClock controls the frequency, and amplitude is dependent on frequency (probing the capacitor with the scope's probe affects the frequency slightly due to probe capacitance).

[David Hess]

W2AEW has an easy square/triangle wave-shaper circuit where you could add output filters to get a sine wave. I'm not sure about getting it to 300khz though.. If you need bi-polar, you can level-shift unipolar to bipolar on the output opamp.

Using a diode bridge to switch currents into a capacitor as W2AEW shows is one of the higher performance options and suitable for operation up to at least 40MHz so 300kHz is not a problem and it used to be the go-to function generator topology.  Using currents and an integration capacitor avoids bandwidth limitations of an operational integrator.  The low capacitance of the diodes lowers the amount of charge from switching coupled into the integration capacitor making compensation of this error more effective.  Both contribute to good control of the triangle wave height which is required for low distortion sine shaping.

Interesting. I've built the integrator triangle wave generator before and have found the the jellybean LM393 comparator's propagation delay seemed to be more of a limiting factor, than the integrator.

The delay through the comparator is a major factor.  Not only does it create a linearity error in the frequency, but it increases the amplitude of triangle wave at higher frequencies because switching happens late and the variation in amplitude increases distortion through the sine shaper.  The delay can be compensated by using a capacitor to create a high pass function between the triangle wave output and comparator so that as the frequency is increased, the comparator switches earlier.

The main downside I can see with the current source/sink solution is, if 50% duty cycle is required, getting the currents to match accurately could be challenging.

In practice the current source and sink are controlled by operational amplifiers making it easy to adjust and balance the symmetry.  At least a 1000:1 control range is feasible yielding 20kHz to 20Hz.

[Zero999]

Here's another thread which may be helpful.
https://www.eevblog.com/forum/beginners/simple-analog-function-generator-design/msg1174548/#msg1174548

I've built one of these circuits before, but don't think I got round to posting any oscillograms. If I can find one, I'll 'scope it any post the results.

[Atom]

If you want a cheap funztion generator you can use an AD9833 it goes on aliexpress for 2.50 dollars but you need a microcontroller to instructions to it,
It can go up to 10Mhz ...here it is someaone that has already done it if you want here's the link

http://www.vwlowen.co.uk/arduino/AD9833-waveform-generator/AD9833-waveform-generator.htm

I've ordered 2 of those right now, planning onto doing a 2 channel waweform generator 

[MarkF]

If you want a cheap funztion generator you can use an AD9833 it goes on aliexpress for 2.50 dollars but you need a microcontroller to instructions to it,

I actually like the AD9834 better.  It gives you the ability to adjust the output level directly on the chip.  Here is the design I've done which will give you 1Hz to 4MHz at 3Vpp output.  I'm currently adjusting the gains and DC offset voltages to the output voltage.  This chip provides sine and triangle outputs and a square wave using the signBit output.  The signBit output is connected to a MCU output to also provide a sync when generating frequency sweeps.

[Kleinstein]

AFAIK the high performance max038 got obsolete quite abrupt because the process used to make it was no longer available to Maxim.

These DDS chips / modules replaced the FGen chips in quite some applications. DDS is probably one reason you don't get those chips anymore.
The rectangular signal directly from the DSS highest bit / sign is usually poor quality with quite some jitter. To get a good quality rectangle it needs the reconstruction filter followed by a comparator.

However showing DDS generators is kind of off topic here. A relatively simple analog replacement circuit might be an option today. However the option for amplitude modulation in the XR2206 is kind of a little difficult. The sine shapers might turn out to be temperature sensitive. Otherwise the analog circuit is not that difficult.

[Atom]

If you want a cheap funztion generator you can use an AD9833 it goes on aliexpress for 2.50 dollars but you need a microcontroller to instructions to it,

I actually like the AD9834 better.  It gives you the ability to adjust the output level directly on the chip.  Here is the design I've done which will give you 1Hz to 4MHz at 3Vpp output.  I'm currently adjusting the gains and DC offset voltages to the output voltage.  This chip provides sine and triangle outputs and a square wave using the signBit output.  The signBit output is connected to a MCU output to also provide a sync when generating frequency sweeps.

Oh i didn't know that,  by the way , why areyou limiting the frequency at 4mhz when it can go up to 75mhz ? It's because you don't need those high freuencies?

[MarkF]

If you want a cheap funztion generator you can use an AD9833 it goes on aliexpress for 2.50 dollars but you need a microcontroller to instructions to it,

I actually like the AD9834 better.  It gives you the ability to adjust the output level directly on the chip.  Here is the design I've done which will give you 1Hz to 4MHz at 3Vpp output.  I'm currently adjusting the gains and DC offset voltages to the output voltage.  This chip provides sine and triangle outputs and a square wave using the signBit output.  The signBit output is connected to a MCU output to also provide a sync when generating frequency sweeps.

Oh i didn't know that,  by the way , why areyou limiting the frequency at 4mhz when it can go up to 75mhz ? It's because you don't need those high freuencies?

See attached app note.
Because I'm only using a 32.768 MHz clock.  A power of 2.