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ADS1291 EMG circuit design help

August 6, 2014, 11:37 am
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Hi all

I have some confusion designing EMG circuit with ADS1291. Please share your valuable opinions.

Application: EMG measuring with 2 electrodes

Chip: ADS1291
Analog power: +1.5~-1.5V(bipolar power supply AVDD:1.5V, AVSS:-1.5V)
Digital power: 3.3V

Questions
1. IN2N, IN2P, PGA2N, PGA2P, RESP_MODN, RESP_MODP
Do these pins should be pulled up high to AVDD or DVDD? <-AVDD
Whate value of a resistor is recommended for weak pull up?

2. Is it necessary to put 1M ohm and 1.5nf across RLDOUT and RLDINV for this application(EMG measuring with 2 electrodes)?
If so do I have to decouple incomming signals with capacitors and biased to RLDOUT with high resistors?

3. Do I have to pull up the VCAP2 as IN2N?

4. If I pull up the PWDN and START pins to DVDD, would it be ok without writing any register and read data as the DRDY falls? I mean reading data at default mode(500SPS).

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Register configuration examples for ADS1298R

August 6, 2014, 3:06 pm
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Hello,

I am using the ADS1298R for a 12-lead ECG application and am having a hard time finding examples of how to configure the devise registers over SPI.

For example:

I have the leads configured as follows: (Same as demo-board)  

If I want to configure the WTC as the combination of IN3P, IN3N, and IN2P, I would send the WREG command with the address of the appropriate registers and the configuration bits - that is where i am getting stuck. There are two configuration registers: WCT1 (18h) and WCT2 (19h). The compactors are WctA, B and C. I am calculating my augmented leads digitally, so I want to power down those options by setting bits 7, 6, 5, and 4 to zero.I want WCTA on, so bit 3 = 1, and to use RA I set bits 2, 1, and 0 to (101) - bit options (0000 1 101) = 0D. Similarly, WTC2 would have both WCTB and WCTC powered on and set to IN2P and IN3P for LA and LL respectively, correlating to bit options (11 010 100) = D4. So I want to write both of these in one Op-code, which I should be able to do since 18h and 19h are cosecutive. The datasheet instructs on the WREG opcode "Write n nnnn registers starting at address r rrrr" in the form "010r rrrr 000n nnnn". In the footnotes it says n nnnn should be the number of registers minus 1.

Would the Op-code I need then be: 0101 1000 0000 0001 or 58 01 (h)?

And would my data then be: 0D D4 (h)? 

Then the big question - how do I actually send this taking into account all the timing considerations, or what is the final coding sequence going to look like?

I am slowly piecing this together (I think) but a few examples would be extremely helpful!

Thank you for the assistance!

- Mike J

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pH measurement with TI's INA116

June 10, 2014, 9:08 pm
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I am trying to implement a pH measuring device with INA116 chip. One of the applications of the chip is pH measurement.

Constrants: pH ranges from +- 430 mV. Max input/output 2 Hz frequency. Gain of 11.5 V/V


PH probe have very high impediance ranging from 100 - 1000 MOhms. So INA116 chip is a good choice.

I have attached a pic of my current ckt. 

Problems I am having right now:

1. Noissy signal. On the output signal, I am getting frequency in thousand to mega Hz.

2. The offset voltage is fluctuating from -800 mV to 300 mV or sometimes stable at -400 mV. Now if I place a .10 uF capacitor between inputs the output goes down to -70 mV. Have a offset is a big problem for me as I need 0 mV offset to start with other wise my pH reading screws up. Is there a way to implement auto-zero input offset circuit.

NOTE: with gain set to 11.53 v/v

3. I don't know what type of (LPF @ 2Hz) filter should I implement to at the input and output to block any noise [ without blocking dc input mV signal] from entering my signal and high frequencies. AC-DC power supply do sometimes introduce 60k Hz frequencies too.

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XTR300 value of RGAIN

August 7, 2014, 5:10 am
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Dear Community

We use the XTR300 as Voltage or Current Output Driver (+/-10V or +/-20mA) in a Standard configuration (Rset = 2k, Ros = 2k, Rgain = 10k).

Because of some heat Problems, I'm trying to reduce the power Dissipation of the device. One Point is the current consumption of the IA, which can be reduced by rising Rgain. But all the electrical characteristics in the datasheet are specified with Rgain = 10k. What could be the consequences if I rise Rgain to 20k? Are there any documents available concerning this point?

Best Regards

Martin

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Op-Amp for voltage scaling

August 8, 2014, 5:05 am
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Hi all,

Samsung would like to scale output voltage of battery of Note PC. since output voltage of battery may put into microcontroller, scaling voltage should be under 3.3V.

the output voltage range which is needed to monitor is 5~10V for 2 cells, 8~15V for 3 cells and 11~18V for 4cells. that is, total output range that should be scaled is 5~20V and output voltage should be scaled proportionall by 3.3V.

To scale output voltage of battery, they used the voltage divider as below circuit. However, it had limitation on ADC in MICOM due to voltage drop, tolerance of resistor and leakage.

So I recommended using a buffer between voltage divider and MICOM and LMP8602 whose input common mode voltage range is -0.3 ~ 27V for 3.3V of VDD (they are going to use 3.3V as VDD of Op amp) is considered.

I would like to know whether LMP8602 is the best solution or not.

Please let me that if  there is the proper solution than LMP8602.

Thank you.

 

Best regards,

Sammy Jeon.  

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ECG Amplifier using INA321 and OPA336

August 8, 2014, 2:43 pm
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I am trying to make a simple ECG amplifier using INA 321 and OPA 336. I am driving this amplifier using a an ECG simulator(http://www.heinstruments.com/ecg-simulator.htm), hence I do not have a right leg drive circuit.
My schematic is attached. I have made the circuit on a breadboard for now, the problem that I have is that it works for a few seconds and then stops. The problem seems to be with the INA321 and the feedback opamp used for the reference. I have attached a snapshot of the scope that shows the output turning off.

Any ideas on why this might be happening?

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ISO124 ; 0.010% max NONLINEARITY

August 7, 2014, 12:09 pm
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Hi,

I'd like to have further details regarding the 0.01% FSR max nonlinearirty of the ISO124.

How to assess it ? What does it represent ?

Thanks in advance.

Paulo.

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why pga309evm can not work after calibration with real sensor?

August 12, 2014, 12:57 am
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1.why pga309evm can not work after calibration with real sensor?    i do  step by step according  guider.

2.when i check the test pin  indicate  pull down the test pin or pull up ? 

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I2C command of OPT3001 [urgent]

August 11, 2014, 11:27 pm
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Dears,

Is there any sample code of OPT3001?

My customer test OPT3001 EVM and would like to implement OPT3001 on their system.

However, there is something wrong with the I2C read/write command.

They cannot get the ACK from OPT3001 and below are their I2C code and questions.

1.Do we need write configuration register at I2C initial section?

2.According the I2C example figure, is it still send 4 byte at send Address 00 for read result lux value?

 


Is there any problem with the code?

Thanks.

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LMP91000 -- has anybody used this chip with a 4-terminal eletrochemical cell?

September 13, 2012, 4:03 pm
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Hello,

    The LMP91000 is a nice chip (and even has internal temp sensor which is very handy for EC cells) but it's designed for 3-terminal EC cells.

    However, our application requires more precise measurements and we are trying to use the new 4-terminal EC gas sensors. The 4th terminal is an auxiliary electrode which corrects for voltage drift:

http://alphasense.com/alphasense_sensors/B4_sensors.html

for example: http://alphasense.com/pdf/COB4.pdf

Has anybody successfully used the LMP91000 with a 4-terminal cell?

We are currently planning to just connect the 3 standard electrodes to the LMP91000 and then just run the 4th auxilliary electrode directly into the ADC on our microcontroller, so we can do a correction in firmware;  but if there is a better way to do it, we would be interested to hear from other research folks.

thanks,

-RF

TagSense, Inc.

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digitizing analog 100mV p-p signal

August 3, 2014, 4:11 am
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Hi

I am trying to apply zero crossing detector using lm211.

this is my signal but I cant get this circuit to do what I want.

I connected emiter out, in- and vcc- to  gnd. in+ to the signal below. collector out and vcc+ via 20kohm resistor as shown in page 11 of that datasheet but the output is on high all the time.

why isnt it works?

is there a better way to do what I want (the smaller cheep is the better).

thanks in advanced,

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Need low cost replacement circuit for XTR101

August 12, 2014, 11:41 pm
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Hello TI,

We are using XTR101 chip for RTD to 4-20mA current conversion. We are almost using 1k+ volume per month & we have 5k stock.

The cost of the chip we are getting around 560 Indian rupees for 1k volume. The performance, reliability & repeatability of the chip is excellent. Now we are try to reduce the price of the components. So can anyone suggest a best replacement of XTR101 circuit with lower cost. 

Specification : RTD input 0-150°C to 4-20mA current output. Supply 24V.

Thanks in advance

Regards

Udhay

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INA128 output problem

August 13, 2014, 11:25 pm
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Hi,

I want to use an INA128 to amplify signals from a pressure sensor in the signal range +/-50mV to an output of +-10V. I have built a circuit according to the design in the data sheet using +/-15V supply and a potentiometre to fine tune the gain to 200. The problem is this, the gain varies a lot depending on what signal i put to the amplifier, approximately between 178 and 205 or so. I have tried to use different supply sourses ans different singal sourses. What can be causing this?

Hope you can help!

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power supply low noise amplifier

August 14, 2014, 5:09 am
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Hi all,

I am currently developing an amplifying chain with 90dB gain because the input signal is some microvolt and the desire bandwidth is from 20kHz to 200kHz. To do this I have designed a chain of 4 sallen key with ada4898 operational amplifier.

I notice that the output signal of the amplifying chain is saturated (from -5V to 5V) when the input is shorted to ground.

I think that this noise is due to the power supply.

I use a UA78M05 to provide the +5V and a LM2663 to provide the negative voltage -5V.

In purple it is the positive voltage, in green the negative voltage and in yellow it is the output of the first stage ( gain of 30dB) when the input is grounded.

Reducing the variation by adding a capacitor is not working.

I would like to know if there is an solution to reduce this noise.

Are the power supplies not correctly chosen ?

I had the idea to use voltage reference to power the op Amp. Is it a good choice?

Thank you for your help,

Kind Regards,

Florian

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Minimum TIA gain on LMP91000

August 14, 2014, 8:24 am
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Hello,

Is there a minimum external resistance for the LMP91000 TIA gain? I would like to use a 10 ohm external resistor with no internal resistor in parallel. I wasn't sure that would be too low of a resistance to use.

Thanks for your time.

Theresa

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Writing to PGA117

August 15, 2014, 9:31 am
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Hello,

On page 27 of the PGA117 family datasheet, it has SPI commands for the PGA112/113 and also daisy-chain commands but I don't see where it specifically states what commands I would use for the PGA117. I would like to mux CH9 with a gain of 1. I tried writing 0x2A and 0x09 and also 0x3A and 0x09 but that didn't work. I didn't read anything about these commands writing to registers so I was wondering if there was a way to check whether or not I sent these bytes correctly without having to scope the SPI lines directly. Thank you for your help.

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Operating Temperature Range of INA197AIDBVT

July 5, 2013, 4:37 am
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As per the data sheet, it is provided that the operating temperature range is -55 to 150 and storage temp range is -65 to 150.

But in the website, it is mentioned that operating temperature is -40 to 125. Which data is correct and to be taken for design?

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PGA117: How to verify SPI sent correctly?

August 18, 2014, 1:20 pm
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Hello,

I currently am trying to write to the PGA 0x2a and 0x09 (mux CH9 with gain 1). Here is the scope snapshot of what I am sending to the PGA:

 http://imgur.com/rZo8slL.

However, I am unable to get anything out of Vout. On Page 27, there are SPI commands for the PGA112 and PGA113 but I don't see the commands for the PGA117. Are they the same? If not, where is the reference for the SPI commands to send to the PGA117. Thank you.

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TLV2374 absolute maximum rating voltage of output?

August 17, 2014, 7:16 pm
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Hi, TIers

How much voltage TLV2374 could accept on output pin?

Thanks and best regards.

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PGA309 question of EVM

August 17, 2014, 8:32 pm
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