Validation Devices - Oscillioscope

One of the most important validation devices is Oscilloscope. Raging from graduate to hobbyist and technical guy everyone must have oscilloscope. Oscilloscopes basically are analog or digital type. The age old CRT based scopes mostly used in educational institutions are analog type. The modern scopes are all digital type. The main difference between analog and digital scope is that in a analog oscilloscope measured analog signal is directly applied against a time base where as digital oscilloscopes sample the signal and process before displaying them. An analog  and it has vertical, horizontal amplifier and other circuitry where as digital oscilloscope has sampling circuitry, signal processor and advanced displays with good resolutions. Before going further let us define what an oscilloscope is, in few words. A oscilloscope is nothing but a measuring instrument which gives a visual representation of electrical signal. This visual representation helps in debugging the circuit. An oscilloscope measures signal in a graph of voltage vs time.

Want to buy a oscilloscope from market for your debugging purposes? then you have to consider following criteria:

1. Bandwidth

2. Channel count

3. Sampling Rate

4. Memory Depth

5. Triggering capability

6. Probes and their types

7. Resolution of display screen

8. Connectivity of scope like USB, GPIB, serial port, Ethernet, Etc

9. Analysis of signals

10. Memory Depth

11. Pricing

12. Oscilloscope type

13. Accuracy of measurement

14. Vendor ratings

15. Test suits available

Let us assume you want to measure a 1 MHz signal with scope then you must a scope of 5 MHz min. band-width. the rule of thumb is that bandwidth of the scope must be 5 times of the signal to be measured. The reason for this is that the energy of signal is distributed among it's harmonics and it needs minimum of 5 harmonics for the signal to be reconstructed properly. 

Sampling rate is inverse of the signal to be measured. If we want to measure the 1ns signal over a scope the sampling rate of that scope must be minimum 1Msps.

Channel count defines the number of signals that can be captured in parallel. Based on your requirement choose the scope. Note that if you are using a scope at maximum sampling rate, the rate will be divided as per the number of channels used.

Memory depth measured in Kpts, Mpts defines the amount of storage capability of oscilloscope.

You might have seen x1, x10 marking on the probes. this represents the attenuation. If you take a signal of 1 volt and measure with x1 setting, then the attenuation is 0 and you see a exact representation of 1 volt an the screen. If you use the same scope with x10 setting, then you see 0.1 volt on the screen.

Before buying a scope check the support for communication interfaces like USB, GPIB, ETHERNET, serial ports. Pricing always as per the interfaces available.

Vendors like Agilent, Tektronix, Lecroy, Fluke, Instek are leaders in market and choose a vendor as per your choice. Check the support and servicing facilities of these vendors before making a decision.

Sometimes, you may need special test suites for signal integrity analysis of high speed interfaces like USB, PCIe, etc. These are additions to the scope and if miss them on a buy, you may may have to shell out additional amount later. Also, check out if the vendor is providing free add on boards or on discounted price which are used for these analysis purposes.