Thread for designing an oscilloscope.

[William Gaatjes]

I thought it could be fun to start a thread with such information and to continuously update it with progress. Feel free to join in.


Background information :
http://www.hobbyprojects.com/oscilloscope_tutorial/oscilloscope_working.html

Basic analog oscilloscope :

Basic digital oscilloscope :

To create a proper analog frontend of an oscilloscope, any old analog design will do of an old analog 25MHz/50MHz/60MHz or 100Mhz oscilloscope. Use some modern components in the design and it could be a good start.

When wanting to make a digital oscilloscope, it is very important that there is a relation between the sampling rate and the timebase. We want the sampling rate as high as possible because then the horizontal (time)resolution increases as well, which makes it possible to see hf glitches in the signal. And we want a known preset relationship between the sample rate and the time base. This relationship is a compromise of maximum sample rate together with the available amount of memory to store the digitized signal we want to examine. The time base produces the horizontal sweep in an analog oscilloscope. In a digital oscilloscope it is also present but does not provide a sweep signal. It does however produce time information. The screen is divided into sections such a volt/div and sec/div. This is called the oscilloscope graticule. The time base adjust the value for the sec/div sections. The setting of the amplifier/attenuator section in the analog frontend determines the volt/div. As we will later see in another post, we also have to establish a relationship between the resolution of the analog to digital converter and the volt/div setting. The better(higher) the resolution, the more voltage level information we can capture.

For to make the time base or to make a signal wave generator (ofcourse with added components to adjust signal voltage level and adjustable low pass filter), the AD9834 in combination with an FPGA (and programmable PLL for the ADC) is very usable :

The AD9834 is a 75 MHz low power DDS device capable of producing high performance sine and triangular outputs. It also has an on-board comparator that allows a square wave to be produced for clock generation. Consuming only 20 mW of power at 3 V makes the AD9834 an ideal candidate for power-sensitive applications.

Capability for phase modulation and frequency modulation is provided. The frequency registers are 28 bits; with a 75 MHz clock rate, resolution of 0.28 Hz can be achieved. Similarly, with a 1 MHz clock rate, the AD9834 can be tuned to 0.004 Hz resolution. Frequency and phase modulation are affected by loading registers through the serial interface and toggling the registers using software or the FSELECT pin and PSELECT pin, respectively.

The AD9834 is written to using a 3-wire serial interface. This serial interface operates at clock rates up to 40 MHz and is compatible with DSP and microcontroller standards.

The device operates with a power supply from 2.3 V to 5.5 V. The analog and digital sections are independent and can be run from different power supplies, for example, AVDD can equal 5 V with DVDD equal to 3 V.

The AD9834 has a power-down pin (SLEEP) that allows external control of the power-down mode. Sections of the device that are not being used can be powered down to minimize the current consumption. For example, the DAC can be powered down when a clock output is being generated.

The part is available in a 20-lead TSSOP.

Applications
Frequency stimulus/waveform generation
Frequency phase tuning and modulation
Low power RF/communications systems
Liquid and gas flow measurement
Sensory applications: proximity, motion, and defect detection
Test and medical equipment

http://www.analog.com/en/rfif-components/direct-digital-synthesis-dds/ad9834/products/product.html

The AD9833 is the 12,5Mhz(25Mhz) version.

 

[AD5MB]

there are many Tektronix scopes on ebay for $100 or less. can't see the point in kludgeing junk together when you can have a big dog on your bench for a Benjamin.

now if you could get serious bandwidth and voltage capability and the ability to store the output on a network drive, that would be something worth having. Something that displays on a PC.

 

[santuitman]

Not to steal thread but check this out

http://www.gabotronics.com/product-info/the-xprotolab.htm

 

[Onceler]

the analog BW is only 200KHz

 

[Eriesteamer]

to the ebay guy I got a technics dual scope and 100 bucks on ebay that be the day I every sell mine for 100. there not made for last ( beats me ) years and are now anquteus last I knew and theres a place buy them as that but 100 at least for my dual would be a steal. I have lot TV repair stuff as ran a TV repair shop 50 years. To the buy one thing your wright on that. Im with you. the tech like I got is wide band and run circles round the thing he was talking about.
To thing he was refere to what is the price. last I look up the spect as he had it in post and bass my run aroud on the technics and what the thing he was talking about. and seen no mention of prices.
I like play with the scope I got just bring back old rememberances. my RCA meter and scope and geezz some car full other stuff put food on my table and the green salade ( money ) in my pockets. mmmm As I am today I say I am only one that can fix old radios and TVs. and got tube testers and tubes if they need that plus a few other parts to do a repair job.all TV shops here and you name it folded I was last in this area to drop out. but not sell any my stuff no way. I had a big idea but never put it in action but I tell you it. any one have old car need the radio fix better get to me as I am the guy for that.any one got one give you 100 for a radio for his old car as fast as you can snap your fingers and with a smile on his face. every so often I see old car radio and lot table and floor ones at flea markets that do not work and there asking a lot for them.