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# shekhar_dandya

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• Birthday 05/11/1983

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1. ## Cutoff frequency and 3dB points

Hi All, I may not be 100% correct,but,a loss of 3db in gain does not hamper the overall response of the amplifier.i.e this loss is unnoticable in the o/p of amplifier.But we get higher bandwidth at peak- 3db gain,compared to bandwidth obtained considering only the flat portion of the gain-frequency plot. I would like someone to give more explanation of it.
2. ## Set up time and Hold time

Hi Shiva, The set up and hold requirements stem from the fact that if 2 logic signals change simultenously at the input of a digital sequential circuit there is a possiblity of metastability.Which physical phenomenon is responsible for that I still don't know,if anybody on the forum knows,I will be glad to understand. But,what is metastability?A metastable state is a stable state between logic 1 and logic 0.A digital sequential circuit has not 2 but 3 stable states where it can reside for indefinite time.So if circuit resides in this metastable state i.e between 1 & 0,for eternity,the further logic computation will hamper.Both Q and nQ o/p's of a flipflop assume same value which dose'nt correspond to valid 1 or valid 0. Theorotically a circuit resides in this state for eternity,practically,due to noise,which adds to say,Q output of a flip flop and subtracts from nQ output or vice versa,and due to positive feedback,circuit comes out of metastable state and Q assumes a logic 1 and nQ assumes a logic 0 or vice versa. mathematically,the equation for a stable state is satisfied at logic 1,logic 0 and at a voltage midway between 1 & 0. So to avoid metastability,one input is allowd to change first and second later,giving rise to set up and hold times.These have to be kept to minimum to increase speed,so datasheets specify a min value for both. more inputs from other members of the forum welcomed. Shekhar
3. ## Understanding test conditions in any Datasheet

I went through the pdf.It definitely helped me. comming back to the question, So should I take these "test conditions" in my design and calculate other parameters of my circuit?
4. ## Understanding test conditions in any Datasheet

Hi H.W.Wizard, I did not get you. ???Can you be more elaborate?
5. ## Understanding test conditions in any Datasheet

Generally all parameters of a device in any datasheet are specified at certain test conditions. my question is : 1) How are these test conditions chosen?what criteria? 2)What is their importance? 3) What values of parameters should we select if these test conditions do not exsist in our circuit?
6. ## Basic Transistor Circuits questions

But How does one decide Q point Ic i.e dc Ic?I find many students assuming Ic of 1 mA,just because its fairly a reasonable value. So,when to use say,Ic of 1mA when to use Ic of 10mA or 100mA?
7. ## Basic Transistor Circuits questions

While designing a transistorised circuit,say a voltage divider bias,an amplifier etc,should we select the transistor first and then decide the Q-point characterstics based on its datasheet or we establish the q-point characterstics and then select a suitable transistor? If condition2 is correct,then what values to select for Ic for say a CE voltage amplifier?deciding that Vce = 1/3 Vcc?leaving 1/3Vcc across Rc and 1/3Vcc across Re?
8. ## when should use FPGA?

Ante, If this is meant to be only for MCU's then plz create a forum for
9. ## How to make RPM counters

This method will work for slower RPM, for faster ones? I think then one can measure no. of revs in say 10 sec and then calculate for 1 min? what do you say?
10. ## How to make RPM counters

How to make an RPM counter? Assuming you have some sensing mechanism,say a flywheel with a slit to pass the light beam that is sensed by a photosensor at reciever end and which is attached to a transistor driver that gives you square pulses for every cut. How to process the rest of the signal using a microcontroller? One way is to use interrrupt pin to interrupt the MCU every time the pulse comes and increment a variable in the ISR. use a timer to generate a delay of 1 min.read the counter variable before starting the timer and after 1 min.take the difference and display. Is there any more better way? How are commercial RPM counters/taechometers made? I feel they don;t wait for 1 min to gather the # of revs in a minute. How do they work?
11. ## 'potential Difference' questions

So,motion of electrons constitute current.Hence its current that creates "potential Difference",right?or is it that "potential difference" causes current?Is this that-first egg or chicken problem? BTW I still don't understand the basic origin of Energy in a battery,exactly which chemical energy is released to convert to potential energy? What is EMF?What is its cause?I learned this concepts in junior college but never thought on it deeply,so forgotten.can ne1 explain?
12. ## 'potential Difference' questions

If voltage is potential Energy difference,where does this potential energy come from in batteries or cells?If the answer is "chemical reactions" then which chemical reactions/physical phenomenon(bonding,thermodynamics?) is responsible to impart this "potential energy" to electrons?
13. ## International Physics olympiad problem

solve this international olympiad prob suppose a cylinder of weight 20N is rolling on ground in right direction.if half of length of cylinder is positively charged,and it is placed in magnetic field whose dirction is inward to plane of rolling and if a charged particle is placed at distance 10m from cylinder .and magnitude of electrical interacton is 10N and magnitude of magnetic field force is 31N. will cylinder fly? if yes ..then in which direction ? I tried to solve this: Basically the cylender will fly if normal component of net force acting on cylender is > 20N. I found many things missing in the above problem or they need to be assumed: 1.Polarity and magnitude of charge(+ve/-ve)? if we use F = q1q2/r2(coloumb's law) how to find q1,q2? 2.Placement of charge in 3-D space? 3.The mechanical force acting on the cylender due to magnetic field: F = BILsin(x). How to find B from magnetomotive force? B = uH H = mmf/(leghth of coil).How to find this? 4.The velocity at which cylender is rolling?From this we could find the current i.e rate at which charge is moving. I think x = 90 deg so sin(x) = 1. Any thoughts? -Shekhar
14. ## Voltage

"Potential" of a point in space,as I was taught in school, is energy spent in bringing a charge from infinity to that point within the vicinity of test charge,which is exerting the force on our charge. So energy spent is stored as
15. ## Simulation Models Creation...

Try downloading Labcenter electronics evaluation version Proteus software from their website.It internally uses PSpice.I foud it very handy for microcontroller based simulations...hope you will also find it useful.
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