Other Parts Discussed in Post: LMP91000, AFE4300, AFE7070, AFE4490

The Adventures of the COFIE Club

Episode I - The case of the analog front end

C.P. Ravikumar, Texas Instruments

Art by Ananya Ravikumar

When I visit campuses and interact with students, I often ask them to raise their hands if they wish to turn into entrepreneurs sometime in the near or distant future. After a delay of few seconds, a couple of hands go up. I push these students into answering more questions on what products they are thinking of, or what application domain excites them. If I hear only silence, I promise the students that I will not steal their ideas. I hear a few chuckles. This usually breaks the ice. 

A decided to write a fictitious account of a student who wishes to become an entrepreneur in the near future. The moral of the story (stop groaning) is that entrepreneurs have a lot of think about, and a lot of it is analog in nature. There is also a quiz at the end of the story! Feel free to use the Internet resources to answer the quiz, but remember that the real intent here is to make you read than to fish for answers. 


The COFIE Club

Rahul is an undergraduate student of engineering and likes to dabble in “Do It Yourself” electronics. He dreams about starting his own company which will manufacture products for the global market.  He is full of ideas, but is looking for a product that will not only help the society, but will also be commercially successful. Rahul has many like-minded friends and when they are not meeting for coffee, they are conversing on a social medium. They call themselves COFIE (club of future innovators and entrepreneurs). At present, there are five members in this club, including a Beagle named Timmy.  You will meet them soon. If you are noticing many similarities between between COFIE club and the “Famous Five,” you may be on to something.

On a Sunday afternoon, the members of COFIE met and the topic of discussion was (surprise surprise) what was the product they were going to make when they would graduate in a year.

Sahil, who had just come from a gym, volunteered. “Today, my gym instructor told me that reducing your weight is not the only important thing. What is important is your body composition – how much of it is fat and how much of it is muscle. What if we build a machine that can measure the body composition?”

“Good thought! Alas, my search engine says that such machines do exist,” said Simran, pointing to her tablet PC.

Rahul was not easily discouraged. “That need not deter us. Remember, the key is innovation – we can innovate in so many ways! We could reduce the cost and make this machine pocket-sized, for example!”

“Woof! Woof!” agreed Timmy.


Did any body say measurement?

“Agreed! Suppose our machine can display the body mass index and weight!” said Milind. “There was this student team from NSIT that built a weighing machine which could speak in several languages! This was an entry in TI India Analog Design Contest! Imagine a machine that tells you that you are fat and overweight in your own language!”

“Listen to what Internet has to say,” said Simran. “On an average, about 57% of the body weight of an adult consists of water. Obesity decreases the percentage of water content in the human body.  If we can estimate the percentage water in human body, we can actually make an obesity meter.”

“Or make a machine that separates juicy apples from the starchy ones, perhaps!”

“Every fruit vendor will want one of those!”

“Let us look at a more serious application – how about a meter that shows if a child is suffering from malnutrition?” said Sahil.

“Every school would like to have one of our gadgets!” Rahul enthused.

“Here is more information!” Simran continued. “The phase angle of the body impedance reflects the relative contributions of fluid (resistance) and cellular membranes (reactance) of the human body and has been suggested to be an indicator of body cell mass and nutritional status.  The phase angle of the body impedance may be a useful indicator of several ailments.”

“But wait, how do we measure the water content in the body?” asked Simran.

“Internet to the rescue!” someone shouted, and you know who that is. “Water offers lesser impedance to electricity than fat and bones.”

“So all you have to measure is the body’s impedance!” Rahul interpreted.

“Wow, I have been measuring my body resistance using the multimeter in the lab! Not knowing that there is a purpose to that measurement!” Milind exclaimed. 

“I bet the resistance was in several mega ohms!” Simran teased. “You eat such greasy food in the Dhaba every day! And as far as weight goes, they will need to put a different scale for handling users like you!”

“Not fair! I suspect the acceleration due to gravity has been increasing, these days. How else can I explain my weight gain?”

“OK, that’s enough! Put on your thinking hats, folks! How does one measure impedance? Until we figure that out, our discussion holds very little water!”

“Woof! Woof!” said Timmy, reminding the rest of them that he was hungry.


You can help COFIE Club

The story does not have to end here. You can help continue this story further. You and your friends may have a COFIE Club of your own! If not, it is never too late to start one. TI helps young innovators in the college through an initiative called “Texas Instruments Innovation Challenge.” Under this initiative, TI holds design contests in many geographical regions. In India, we will announce the “Texas Instruments Innovation Challenge: India Analog Design Contest 2013-2014” in the month of April. You may already know about the TI India Analog Design Contest from previous blogs.  The 2012-2013 contest is in its final phase and we expect to announce the final results at the award ceremony to be held as part of TI India Educators' Conference.  If you want to see some of the innovations from the Indian campuses, I invite you to view these videos.

Let us return to the ideation exercise of COFIE club. Imagine that by some magic or through virtual reality, you have entered the meeting of the COFIE club. Help answer the questions below.  Fishing out answers is only the first step.


Quiz!

Q1: Which of the following integrated circuits from Texas Instruments would be an ideal choice for building the analog front end for COFIE club’s application?

(a)   LMP91000

(b)  AFE4300

(c)   AFE7070

(d)  AFE4490

Q2: The integrated circuit which you selected in Q1 above measures the body composition by measuring the body impedance by applying a sinusoidal current to the body and measuring the voltage developed. Remember that impedance has two components, resistance and reactance. To measure this, the technique used in the IC is

(a)   Use a fixed-point divider to compute |Z| = V (rms)/I (rms) and using a PLL to measure the phase of the impedance

(b)  Use a complex divider to compute Z = V/I

(c)   Use an IQ modulator to estimate the In-Phase and Quadrature parts of the voltage across the body resistance

(d)  All of the above methods, depending on the accuracy desired

Q3: Which of the following analog components is not used in the analog front end?

(a)   Digital to Analog Converter

(b)  Differential Amplifier

(c)   16-bit SAR analog-to-digital converter

(d)  Full-wave rectifier

Q4: At any time, the COFIE club’s gadget will be used either as a weighing scale or as a body composition meter.  How can the AFE take advantage of this fact to reduce cost and power dissipation?

(a)   Sharing the built-in DAC

(b)  Sharing the built-in ADC

(c)   Putting the portions of the circuit that are not used at the time into sleep mode

(d)  Reconfiguring the same transistors to achieve both functionalities

Q5.  If a microcontroller has to read the data from the AFE to display it on an LCD interface, then

(a)   the controller has to use the SPI interface supported by the AFE

(b)  the controller has to use the I2C interface supported by the AFE

(c)   the controller has to use the ZIGBEE interface supported by the AFE

(d)  the controller can use any one of the above interfaces, all of which are supported by the AFE

Q6. The DAC (Digital to Analog Converter) in the AFE is useful for

(a)   Generating the sinusoidal current which must be passed through human body for body impedan\ce measurement

(b)  Generating a DC value for offset cancellation in the weighing machine application

(c)   Both (a) and (b)

(d)  Neither (a) nor (b)


Anonymous
  • 1--(b)  AFE4300

    2--(c)  Use an IQ modulator to estimate the In-Phase and Quadrature parts of the voltage across the body resistance

    3--(c)  16-bit SAR analog-to-digital converter

    4--(c)  Putting the portions of the circuit that are not used at the time into sleep mode

    5--(a)  The controller has to use the SPI interface supported by the AFE

    6--(c)  Both (a) and (b)

  • 1. (b)  AFE4300

    2. (c)   Use an IQ modulator to estimate the In-Phase and Quadrature parts of the voltage across the body resistance

    3. (c)   16-bit SAR analog-to-digital converter

    4. (c)   Putting the portions of the circuit that are not used at the time into sleep mode

    5. (a)   the controller has to use the SPI interface supported by the AFE

    6. (c)   Both (a) and (b)

    DEBOPAM GHOSH

    HERITAGE INSTITUTE OF TECHNOLOGY, KOLKATA

  • 1. (b)  

    2. (c)

    3. (c)

    4. (c)

    5. (a)

    6. (c)

    Ankur Hasija

  • 1. (b)  AFE4300

    2. (c)  Use an IQ modulator to estimate the In-Phase and Quadrature parts of the voltage across the body resistance.

    3. (c)   16-bit SAR analog-to-digital converter.

    4. (b)  Sharing the built-in ADC.

       (c)  Putting the portions of the circuit that are not used at the time into sleep mode.

    5. (a)  The controller has to use the SPI interface supported by the AFE

    6. (c)  Both (a) and (b)

  • Answers to the questions of the blog are as follows

    Q1.   (b)  AFE4300

    Q2.   (c)  Use an IQ modulator to estimate the In-Phase and Quadrature parts of the voltage across the body resistance

    Q3.   (c)  16-bit SAR analog-to-digital converter

    Q4.   (c)  Putting the portions of the circuit that are not used at the time into sleep mode

    Q5.   (a)  The controller has to use the SPI interface supported by the AFE

    Q6.   (c)  Both (a) and (b)

    Satyabrata