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Visitor uowb4g01
Visitor
10,632 Views
Registered: ‎11-29-2011

How to use the ADC on Spartan 3e kit board?

Hi, I'm using a Spartan 3e kit boart. The ADC part on the board is consisting of a AMP and ad. From the UG230,  the input analog signal must be in the range of (0.4v~ 2.9 v)? The peak-to-peak value of  the signal I want to send it into the board is around 0.2 v. So what should I do? Another a circuit to amplify it? THX

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8 Replies
Teacher eteam00
Teacher
10,626 Views
Registered: ‎07-21-2009

Re: How to use the ADC on Spartan 3e kit board?

  • The input range of the ADC is ± 1.25V (or 2.5V P-P).
  • Your input signal is 0.2V P-P

Therefore, to avoid clipping, the gain supplied by the programmable gain amplifier must be no greater than

 

2.5V

----  = 12.5

0.2V

 

The nearest gain setting value is -10 (UG320 Table 10-2).

 

Your 0.2V P-P input signal should be AC-coupled to the programmable gain amplifier, with a DC bias to REF voltage developed by divider R132+R129 (schematic sheet 11 of 14).

 

Using Equation 10-1, the resulting range of input values from the ADC should be

 

                 VIN - 1.65V                    ± 0.1V

D[13:0] = GAIN x ----------- x 8192  = [-10] x -------- x 8192 =~ ± 6553(d)

                    1.25V                       1.25V

 

The ADC output (14-bit 2s complement) value should range from 0x2667 to 0x1999, or  ±1999(h).

 

This topic belongs in the Xilinx Boards and Kits forum.  The Spartan Family FPGAs forum is for discussing technology and implementation details which are specifically related to the Spartan devices and packages.

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
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Visitor uowb4g01
Visitor
10,617 Views
Registered: ‎11-29-2011

Re: How to use the ADC on Spartan 3e kit board?

Thank U very much! I'm searching and reading the datasheets of these three,  2624, LTC 6912-1 and LTC 1407. So should I use an extra power supply  to provide a 1.65 V to the J7 header's REFAB? I measured the VCC and GND and found out its voltage is 3.3 v. Does  that mean there's no need that I add a VCC to the J7?

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Teacher eteam00
Teacher
10,614 Views
Registered: ‎07-21-2009

Re: How to use the ADC on Spartan 3e kit board?

So should I use an extra power supply  to provide a 1.65 V to the J7 header's REFAB? I measured the VCC and GND and found out its voltage is 3.3 v. Does  that mean there's no need that I add a VCC to the J7?

 

You haven't explained why you are asking these questions, so I'm unsure how to answer.

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
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Visitor uowb4g01
Visitor
10,611 Views
Registered: ‎11-29-2011

Re: How to use the ADC on Spartan 3e kit board?

Hi, I want to make the ADC part work for the signal which is obtained from a sensor. The p-to-p voltage is around 0.2 v, and according to your reply, I know the gain setting of that pre-amp on the board. But what I don't know, these 6 pins in J7 on the kit board, REFAB, REFCD,VINA, VINB,  VCC, GND , what should they be connected to ?

Regards.

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Teacher eteam00
Teacher
10,607 Views
Registered: ‎07-21-2009

Re: How to use the ADC on Spartan 3e kit board?

J7 pin/signal      connection

  REFAB              none

  REFCD              none

  VINA             sensor output (AC-coupled?)

  VINB               none

  VCC                none

  GND              sensor GND

 

Remember that your sensor output signal must be centred around the REF input to the programmable gain amplifier.  The easiest way to ensure this is to AC-couple the sensor output (to J7 pin), and add a high-value R (as a DC bias) from the REF voltage to the PGA side of the input cap used for AC coupling.

 

Remember:  AC-coupling implies a high-pass filter applied to the output of your sensor.  Is the sensor output a DC signal or an AC signal?

 

Does this make sense?

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
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Visitor uowb4g01
Visitor
10,604 Views
Registered: ‎11-29-2011

Re: How to use the ADC on Spartan 3e kit board?

Thx very much. I'll try it. It's an AC signal.

Cheers

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Visitor xyjimmy
Visitor
10,346 Views
Registered: ‎07-12-2012

Re: How to use the ADC on Spartan 3e kit board?

Hello Sir,

 

I try to use Spartan 3e kit borad to captuer a sine signal, but when I add some bias to the signal, the analog value changes. For example, the input is y=0.4+sin(x), which means the peak value should be 1.4 volt. However, when I connected this signal to VINA on the board and turn on the board, the peak value reaches to 1.7 volt.  I set the gain as -1 and all values have been observed with scope.

 

By the way, if I give DC value or sine signal, it works very well, so I don't think there is any problem for my code. Is that because I mix AC and DC? However, I must need them mixed for my project.

 

Thanks. 

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Teacher eteam00
Teacher
10,333 Views
Registered: ‎07-21-2009

Please start a new thread

Jimmy,

 

Welcome to these forums.  Please take the time to read the New Users Forum README thread.  There you will find the following:

 

4. Please do not post a new topic or question on someone else's thread -- start a new thread!

 

Interrupting a discussion with an unrelated topic or question is not simply rude, it is considered disrespectful.  This is called hijacking.

  • If your question or topic is unrelated (and unhelpful) to an existing thread, please start a new thread.
  • We want to avoid unreadable threads with 100s of posts which cover topics ranging from power supplies to memory controllers.  Such threads are of no benefit to the users who will follow after you, and a disservice to the creator of the thread who is also seeking help.

and

 

Development board topics:
care and feeding of ADC, pre-amp, and DAC on many Xilinx development boards link#1  link#2  link#3  link#4

 

Please do not request assistance by way of private messages unless your problem requires privacy or offers fantastic exchanges of wealth.

 

Finally, if your input voltage is too high, you should consider reducing it.  If this is not possible, then consider reducing the input amplifier gain.

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
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