Analog & Digital Communications
Why FM famous ??
In AM amplitude is varied according to the amplitude of the modulating signal. while in FM frequency is modified. Noise waves have amplitude and it can able to change the amplitude of a wave and hence AM waves are affected with noise.ie less audio quality.
As FM wave has constant amplitude, even if it is affected with noise , it can easily removed by clipping and the infornation what we want is inside the frequency of the wave and amplitude variation is not our problem. so FM have very good sound clarity.
As energy of a wave is propotional to the square of its amplitude, we can understand FM has greater power and energy compared to AM ,with same input power.
Stereo transmission of FM is also less complicated as it with AM as interference is minimised.
AM utilises ionospheric propagation while FM , LOS .Due to this range of FM is less compared to AM . But this is an advantage because no. of satations can be increased as interference due to adjacent stations are avoided. As there are more fm stations in a city it is natuarly get famed. Different stations, different music .......so we discards AM.
As FM wave has constant amplitude, even if it is affected with noise , it can easily removed by clipping and the infornation what we want is inside the frequency of the wave and amplitude variation is not our problem. so FM have very good sound clarity.
As energy of a wave is propotional to the square of its amplitude, we can understand FM has greater power and energy compared to AM ,with same input power.
Stereo transmission of FM is also less complicated as it with AM as interference is minimised.
AM utilises ionospheric propagation while FM , LOS .Due to this range of FM is less compared to AM . But this is an advantage because no. of satations can be increased as interference due to adjacent stations are avoided. As there are more fm stations in a city it is natuarly get famed. Different stations, different music .......so we discards AM.
How is mobile charging is done via message? Is it still in progress or it is in practical?
Ok not justified if I leave a lose comment like that.
Battery charging via SMS: Send an SMS to phone, to let all other services such as antenna communication go in a low profile and start the API set of charging the battery UI enabling on the device screen. Start your induction charger from where ever you are. For the practical reasons be within few meters of range. Lets say the whole class in a school can charge their mobiles if they are indeed authenticated via SMS to the network and are allowed to latch on to the charger in question and start charging battery wirelessly. That is possible was demonstrated by MIT team in 2006.
Account charging via SMS: You have account with a company say XYZ, by the action you took SIM card or a CDMA device from them. when you power up the device your device registers with HLR or VLR, and then your info is conveyed to your home network - from where you bought and first registered you phone. Once someone sends you SMS or you receive SMS (by the way phones always have a port open like computer's 8080 port to listen to incoming traffic. SMS are of 3 kinds 0, 1, 2 messages, pop up, store on handset and store on SIM kinds, there is another on that checks if SIM is full goes to handset - another discussion you can read for it). So once you send that SMS out, network charges your account based on your HLR info, to your account on file.
Battery charging via SMS: Send an SMS to phone, to let all other services such as antenna communication go in a low profile and start the API set of charging the battery UI enabling on the device screen. Start your induction charger from where ever you are. For the practical reasons be within few meters of range. Lets say the whole class in a school can charge their mobiles if they are indeed authenticated via SMS to the network and are allowed to latch on to the charger in question and start charging battery wirelessly. That is possible was demonstrated by MIT team in 2006.
Account charging via SMS: You have account with a company say XYZ, by the action you took SIM card or a CDMA device from them. when you power up the device your device registers with HLR or VLR, and then your info is conveyed to your home network - from where you bought and first registered you phone. Once someone sends you SMS or you receive SMS (by the way phones always have a port open like computer's 8080 port to listen to incoming traffic. SMS are of 3 kinds 0, 1, 2 messages, pop up, store on handset and store on SIM kinds, there is another on that checks if SIM is full goes to handset - another discussion you can read for it). So once you send that SMS out, network charges your account based on your HLR info, to your account on file.
1) do u mean u need 10MHz from digital circuitry? or is 10MHz available and u need to derive anotehr freq.
Free running oscillator example is schmitt trigger. another way is using RC ckt followed by gate delays (D f/f's) with source being DC. there r loads of solutions really. u need to be realistic while giving a spec. u have provided a balck box spec.
wat abt ppm (stability of oscillation), source available , max no. of gates that can be used. application it wld be used in, temperature stability (TTL stability is really poor over temperature)
semiconductor materials r quite a lot influenced by temp variations and also to a degree based on stress on ic pins n contacts. (this info is just for future use, dont mind)
Also, transmission lines length matters as the freq generated wants to see a particular load. if the tx'n line is of length at the desired freq such that the capacitance is high, the ckt wld get de-tuned.
So, u need to specify the load and source.
2) y is op-amp used?
read standard op-amp books, its nicely mentioned with applications.
opamp is a typical circuit using differential mode transistors, buffer,etc. which would take loads of board area while assembling and also cost would be high.
the main thing, a typical ckt of op-amp consists of dual i/p, balanced o/p differential amp, dual i/p single o/p diff amp, emitter follower follower (current sourcing capability), buffer stage. Thats not it. Read the datasheet carefully for noise and temperature performance. Its not a piece of cake to do that. so much interaction going on. the bias stages of the opamp consists a lot of constant current sources,etc. which r complex designs. All this to get the circuit (opamp) to work over -40 to +80degrees typically. Try doing that on spice and u wld be amazed.
Free running oscillator example is schmitt trigger. another way is using RC ckt followed by gate delays (D f/f's) with source being DC. there r loads of solutions really. u need to be realistic while giving a spec. u have provided a balck box spec.
wat abt ppm (stability of oscillation), source available , max no. of gates that can be used. application it wld be used in, temperature stability (TTL stability is really poor over temperature)
semiconductor materials r quite a lot influenced by temp variations and also to a degree based on stress on ic pins n contacts. (this info is just for future use, dont mind)
Also, transmission lines length matters as the freq generated wants to see a particular load. if the tx'n line is of length at the desired freq such that the capacitance is high, the ckt wld get de-tuned.
So, u need to specify the load and source.
2) y is op-amp used?
read standard op-amp books, its nicely mentioned with applications.
opamp is a typical circuit using differential mode transistors, buffer,etc. which would take loads of board area while assembling and also cost would be high.
the main thing, a typical ckt of op-amp consists of dual i/p, balanced o/p differential amp, dual i/p single o/p diff amp, emitter follower follower (current sourcing capability), buffer stage. Thats not it. Read the datasheet carefully for noise and temperature performance. Its not a piece of cake to do that. so much interaction going on. the bias stages of the opamp consists a lot of constant current sources,etc. which r complex designs. All this to get the circuit (opamp) to work over -40 to +80degrees typically. Try doing that on spice and u wld be amazed.
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