डिजिटल ऑसिलोस्कोप्स ऐसे उच्च नमूना दर कैसे प्राप्त करते हैं?

Question

डेटा कैप्चर के दृष्टिकोण से, यह कैसे प्राप्त किया जाता है? यदि मैं उच्च आवृत्ति एनालॉग संकेतों को पकड़ने के लिए एक घर-निर्मित डिजिटल डिवाइस को लागू करना चाहता था, तो मेरे पास क्या विकल्प हैं? अब तक, मैं केवल डिजाइन के लिए कुछ काफी बेकार विचारों के साथ आया हूं!

एक PIC माइक्रोप्रोसेसर का उपयोग करते हुए, एक 18f श्रृंखला पर ए / डी नमूना दर मेरा मानना ​​है कि अगर मैं सही (?) हूं तो 10 बिट सटीकता पर 1Mhz के क्रम में काम करता हूं और मैं समर्पित ए / डी चिप्स होने की कल्पना नहीं कर सकता हूं? बहुत बेहतर है, आधुनिक स्कोप कैसे गीगाहर्ट्ज में आवृत्तियों को प्राप्त करते हैं?

Comments

आमतौर पर FPGAs या कुछ अन्य प्रोसेसर का उपयोग बाहरी एडीसी के उस डेटा को संभालने में सक्षम होने के लिए किया जाता है। ऐसा कोई तरीका नहीं है जिससे कोई PIC इसे संभाल सके।

— कालेनजब

हर किसी के जवाब और टिप्पणियों के लिए धन्यवाद, सबसे अच्छा चुनना मुश्किल था, सभी ने मिलकर मेरे सवाल का बहुत अच्छी तरह से जवाब दिया!

— 14:22 बजे CL22

Answer 1

प्रवेश स्तर DSO रिगोल 1052E (एक मैं स्वयं और सॉफ्टवेयर परिवर्तन के साथ 100 मेगाहर्ट्ज सक्षम) एक एनालॉग डिवाइस AD28288 का उपयोग करता है। यह एक दोहरी चैनल एडीसी है जिसमें 8 बिट समानांतर आउटपुट और नमूने 40 या 100 मिलियन नमूने प्रति सेकंड (चिप की गति ग्रेड के आधार पर) हैं। हालांकि रिगोल प्रति सेकंड 1 गिग का नमूना है, इसलिए मुझे यकीन नहीं है कि अगर वे इनको मल्टीप्लेक्स कर रहे हैं या क्या वास्तव में उन्हें सिंगल चिप के 10x नमूने दे रहे हैं।

The AD9288 has bit-per-stage pipeline type converter for the 5 MSB bits and uses a 3-bit flash for the final 3 LSB. This makes sense, as the higher magnitude should be easier to convert fast with pipelines. As your ADC speeds go up, the number of bits sampled via flash conversion will increase, as steven said.

Comments

They do have 5x of these chips (overclocking them overspec to 100Mhz), and they do precise commutation via CPLD, where you can trim delays down to picoseconds.

— BarsMonster

That makes sense. It is capable of 1 Gs/s with single channel, using 5x2channels for 10 samples offset. When you go dual channel is drops to 2x 500Ms/s with each channel getting 1/2 of each of the 5 chips.

— Joe

Answer 2

I presume they use Flash ADCs. These have the advantage that the conversion is immediate, while SA (Successive Approximation) ADCs like used in most microcontrollers perform an algorithm that requires a number of steps. A disadvantage of Flash ADCs is that they are rather heavy on hardware (an 8-bit ADC has 255 comparators), but most scopes don't have very high resolution. (Analog scopes often were 3% accurate, which translates to 5 bit.)

Comments

एक और दृष्टिकोण जिसके बारे में मैंने पढ़ा है, वह है फ्लैश एडीसी और क्रमिक-सन्निकटन के बीच एक क्रॉस करना। एक बार 6-बिट फ्लैश एडीसी और 6-बिट डीएसी का उपयोग करके 10-बिट रूपांतरण प्राप्त कर सकते हैं; फ़्लैश ADC का उपयोग पहली बार इनपुट रेंज को 64 सबग्रेंज में विभाजित करने के लिए किया जाता है, जिसमें DAC तब DAC के एनालॉग वोल्टेज रेंज को उस सीमा के ऊपर और नीचे सेट करता है, जिसमें वह है (सिद्धांत रूप में कोई 12-बिट रूपांतरण उस तरह से कर सकता है, लेकिन ऐसी चीजें प्राप्त करना जो सटीक होना मुश्किल होगा), इसलिए IIRC निर्माता सैद्धांतिक रूप से आवश्यकता की तुलना में फ़्लैश ADC पर एक और बिट का उपयोग करेंगे।

— supercat

Yet another approach which would be possible, though I don't know if anyone uses it, would be to design a chip with multiple slower ADC's in it and have them sample the input at intervals. One might want 500,000,000 conversions/second, but would likely not need to get any particular conversion within 2ns of when the signal arrives; a chip with 10 ADC's each of which took 20ns for a conversion would work just fine might be easier to build than one which could do a single conversion in 2ns. Not sure how much that approach is used, though.

— supercat

Answer 3

Jodes, आपकी टिप्पणी कहती है कि आपको अपना उत्तर मिल गया है, लेकिन फ़्लैश एडीसी की तुलना में समाधान के लिए बहुत कुछ है। एगिलेंट के एप्लिकेशन नोट पर एक नज़र डालें, " ग्रेटर थान 16 गीगाहर्ट्ज़ के ऑसिलिलोस्कोप बैंडविथ्स को प्राप्त करने की तकनीक ।" मैं उस परिसर में काम करता था (लेकिन विस्तृत गुंजाइश का अनुभव करने का दावा नहीं करता)। कोलोराडो स्प्रिंग्स में Agilent बहु-गीगाहर्ट्ज़ सिग्नल प्रोसेसिंग से संबंधित ज्ञान का वैश्विक केंद्र है। उन्होंने वर्षों तक 32GHz समाधान पर काम किया and just started shipping last year. The active probes and microelectronics that do the signal processing are extremely sophisticated. Check out the entire library of documents related to Agilent's Infiniium 90000 X-Series high-performance DSO and DSA oscilloscope. Google it -- the URL is ugly and I'm not sure they offer a permanent link to the library page. You might also want to have a look at the related patents.

Answer 4

Oscilloscope manufactures advertise with 'equivalent sampling rate'. This is NOT a live sampling rate. This is a sampling rate done by using samples of multiple periods, and taking samples at different moment of the signal. Combining these, and you get a higher 'equivalent sampling rate'. So if you would have 100MSPS ADCs and do this 10 times (really bad!) , you get 1GSPS.

This is bad because it assumes your signal is periodic, which it isn't all the time.

What is important of a oscilloscope is the 'single shot' sampling rate. It's also a functionality you are likely to use (capture a step response for example), or have a close look at a non-dancing waveform. It gives an indication what the hardware is capable of, not 'polished' by software. Hardware can be interleaved, i.e. using multiple high-speed ADCs and time the 'start conversion' signals at the right time. This is also the reason why some scopes will have higher sample rates in single channel mode than in dual channel. Your typical PIC18 series only has 1x ADC converter, but multiple channels (done with an analog MUX).

इसके अलावा, समर्पित एडीसी चिप्स बहुत, बहुत हो सकते हैं faster. 100MSPS isn't too awkward to find. Take a look here, National advertises these as ultra high speed. I don't know how they exactly work, I see the 3GSPS ones use internal interleaving already.

http://www.national.com/en/adc/ultra_high_speed_adc.html

Comments

This deserves more votes - DSO's allow the marketing department far too much creativity with the specs compared to analogue scopes.

— John U

Today's inexpensive 1 GS/s scopes actually do sample in real time at that rate, in single channel mode - the other answers explain how it is accomplished by using several phase-staggered ADCs with sample & hold bandwidth far above their conversion rate.

— Chris Stratton

I don't think that there's nearly as much creativeness with specs as this answer implies. Rigol, to give just one example, doesn't advertise "equivalent sampling rate" at all on their low end 'scopes because they don't even have equivalant-time sampling; they're very clear that the rates they're giving are real-time rates, and they compare against real-time rates on competitors' scopes.

— Curt J. Sampson

Answer 5

The Rigol 1052E as mentioned by Joe is a great example of how to do this efficiently and cheaply. It uses a pile of independent ADCs, all of which having a slower sampling rate, and clocks them out of phase with each-other. This way, samples get pulled from each ADC in turn round-robin style.

Obviously your timing has to be extraordinarily precise to do it this way, and it appears that the 1025E uses a PLD to do just that - and given that the same board also has an FPGA associated with processing the incoming signal, it appears that the PLD (which is much less powerful but with more predictable internal routing) was added because of its ability to generate and process signals with very precise timing.

Answer 6

They interleave the multiple adcs with clocks that are slightly out of phase with one another, getting 5x the sample rate of a single chip. Also, for a periodic signal, there is a trick that a lot of modern scopes use which is to have a sampling clock that is out of phase with the signal being measured, so that on successive samples, a different part of the waveform is being sampled, though in a different cycle of that waveform. Then after enough samples are taken, they can then reconstruct the signal if they can determine the fundamental frequency of the waveform being measured (much easier to do). Make sense?