DC Manual Final

PCCOER, Ravet

Department of E&TC

Experiment No.

: 1

Experiment Name

: Experimental Study of PCM and Companded PCM

Class & Batch

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Roll No

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Date of Performance Performance

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Signature

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TE (E&TC) (SEMESTER I)

1

Digital Communication

PCCOER, Ravet

Department of E&TC EXPERIMENT NO. 1

AIM: a) Experimental Study of Pulse Code Modulation & Demodulation b) PCM Companding. APPARATUS: PCM trainer kit, patch chords, CRO, CRO probes. THEORY: a) PCM Modulation & Demodulation: By Nyquist theorem, if signal contains no frequency components for Fs >2f m, it is completely described by instantaneous sample values uniformly spaced in time with period Ts. If a signal has been sampled at the Nyquist rate or greater (Fs > 2f m) & the sample values are represented as weighted impulses, impulses, the signal can be exactly reconstructed from it’s samples by an ideal LPF of  bandwidth B.W. Pulse code Modulation is a digital transmission of samples of analog signal. In PCM Generator we have sampler, Analog to digital converter & parallel to serial data converter & serial transmission. In PCM Receiver there is serial reception of data, this serially received data is then converted to parallel from & then fed to digital to analog converter. The output of DAC is fed to low  pass filter & we get transmitted analog signal. PCM performance as an analog communication system depends primarily on the quantization noise introduced by ADC. In our kit for PCM transmitter we have used ADC0809, Multiplexer IC74151, Latch IC74373, Counter IC4040, IC7404, IC7432 & IC7408 for required Logic implementation. The conversion time of ADC limits maximum sampling rate & therefore Bandwidth of transmitter. All control signals are derived from basic clock. To derive control signals IC7408, 7432, 4017, are used. After analog to digital conversion signals fed to Multiplexer IC. Control for IC 74151 is from IC4040. Every time IC4040 counter gives 8 combinations & transmits 8 bit data corresponding to every sample. In Receiver section we have used shift register IC 74198 in serial in & parallel out form. For synchronization clock at Receiver must be same to clock at transmitter. After serial reception of data

TE (E&TC) (SEMESTER I)

2

Digital Communication

PCCOER, Ravet

Department of E&TC EXPERIMENT NO. 1

AIM: a) Experimental Study of Pulse Code Modulation & Demodulation b) PCM Companding. APPARATUS: PCM trainer kit, patch chords, CRO, CRO probes. THEORY: a) PCM Modulation & Demodulation: By Nyquist theorem, if signal contains no frequency components for Fs >2f m, it is completely described by instantaneous sample values uniformly spaced in time with period Ts. If a signal has been sampled at the Nyquist rate or greater (Fs > 2f m) & the sample values are represented as weighted impulses, impulses, the signal can be exactly reconstructed from it’s samples by an ideal LPF of  bandwidth B.W. Pulse code Modulation is a digital transmission of samples of analog signal. In PCM Generator we have sampler, Analog to digital converter & parallel to serial data converter & serial transmission. In PCM Receiver there is serial reception of data, this serially received data is then converted to parallel from & then fed to digital to analog converter. The output of DAC is fed to low  pass filter & we get transmitted analog signal. PCM performance as an analog communication system depends primarily on the quantization noise introduced by ADC. In our kit for PCM transmitter we have used ADC0809, Multiplexer IC74151, Latch IC74373, Counter IC4040, IC7404, IC7432 & IC7408 for required Logic implementation. The conversion time of ADC limits maximum sampling rate & therefore Bandwidth of transmitter. All control signals are derived from basic clock. To derive control signals IC7408, 7432, 4017, are used. After analog to digital conversion signals fed to Multiplexer IC. Control for IC 74151 is from IC4040. Every time IC4040 counter gives 8 combinations & transmits 8 bit data corresponding to every sample. In Receiver section we have used shift register IC 74198 in serial in & parallel out form. For synchronization clock at Receiver must be same to clock at transmitter. After serial reception of data

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2

Digital Communication

PCCOER, Ravet

Department of E&TC

output of shift register is latched using 74373 & fed to DAC (R-2R Ladder). Output of DAC is fed to filter. To observe stable waveform on CRO the sampling frequency must be exactly integer multiple of signal frequency. In our kit signal frequency is ob tain by frequency divider & filter circuit. BLOCK DIAGRAM OF PULSE CODE MODULATION / DEMODULATION: PCM MODULATOR:

PCM DEMODULATOR

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3

Digital Communication

PCCOER, Ravet

Department of E&TC

PROCEDURE:  Note: Pot provided at top left side corner is for varying dc bias at theI/p of A/D. We can measure DC  bias voltage v oltage at the test pt. 8 bit dip switch is provided for varying bit resolution of A/D. If Sw is ‘ON’ that means that bit is going to latch connected after A/D. If it is ‘OFF’ it means gnd is connected to respective pin of latch. If LSB bit is off (no. 1 of DIP switch) least count of A/D is now 38 mv instead of ‘19mv’ when all bits are connected. connected. 1) Switch on ‘Power on’ switch, red LED should glow. 2) Observe 1MHz clock O/p signal on panel. 3) Connect this 1MHz clock to ADC 0809 clock I/p. 4) Observe point ‘A’ O/p from: 2 Network & connec t it to point ‘B’ i.e. I/p to 8 Network . 5) Observe O/p of both: 8 network & calculate their frequencies. 6) Connect O/p of 2nd: 8 network to start start conversion I/p of ADC 0809 i.e. ‘SC’ point on panel. 7) Observe ‘SC’ point & ‘EOC’ point on panel simultaneously on dual trace oscilloscope & find out conversion period of A/D. Conversion period Time between falling edge of ‘SC ‘SC’ & rising edge of ‘EOC’. 8) Observe ‘EOC’ point & ‘OE’ point i.e. O/p enable pin of 74373 latch simultaneously on dual trace scope. Also observe ‘RST’ point &’Clk’ point of IC 4040 along with ‘OE’. 9) Observe ‘PCM OUTPUT’ point & connect it to I/p to receiver. i e. serial I/p to shift register 74198. 10) Observe ‘CLK’ of 74198 along with ‘Clk’ of 404 0 dual trace scope. 11) Observe ‘LE’ i. e. latch enable pin of 74373 latches next to shift register, with ‘CLK’ of 74198. 12)  Now you can draw timing diagram of the system. 13) Ensure that all 8 bits are connected to latch latch i. e. that all DIP SWs are to on position. 14) Adjust biasing dc voltage to 2.5v with the pot. 15) By using pot provided above ‘DAC’ adjust 2.5v at the O/p of DAC. DAC. 16)  Now vary I/p biasing pot slightly & observe that accordingly DAC voltage varies linearly, on CRO. 17)  Now keep 3 LSB bits SWs to ‘Off’ position & vary I/p biasing voltage, you will find DAC voltage varies in steps. 18) By measuring I/p voltage & DAC voltage we can find out quantization noise. TE (E&TC) (SEMESTER I)

4

Digital Communication

PCCOER, Ravet

Department of E&TC

19)  Now keep DC bias to 2.5v using nearby pot. & all DIP SWs to on position. 20) Two generators are provided on panel rightmost is fixed frequency Sine wave & the other is variable frequency. (Sine, square & triangular wave generator) To vary its frequency pot is  provided on panel. 21) First Connect fixed frequency sine wave to I/p of ADC 0809. 22) Observe DAC O/p. Calculate its frequency & p eak to peak amplitude. Observe this with I/p fixed frequency sine wave. 23) Connect DAC O/p to I/p of filter & observe O/p of filter. 24) Repeat step 22-23 variable frequency sine, triangular & square wave a I/p to ADC. 25) First keep the frequency of sine wave minimum. Observe the DAC O/p along with I/p sine wave.  Now slowly increase the frequency of sine wave to verify Nyquist criteria and to observe aliasing effect.

OBSERVATION TABLE: Measurement of Quantization Error: Sr. No.

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I/P

O/P

uantization Error = O/P - I/P

5

Digital Communication

PCCOER, Ravet

Department of E&TC

WAVEFORMS: Draw the following waveforms: 1. I/p signal 2. Start of Conversion & End of Conversion 3. O/P enable & PCM 4. LE signal 5. DAC O/P signal 6. LPF o/p.

CONCLUSION:

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6

Digital Communication

PCCOER, Ravet

Department of E&TC

b) PCM Companding AIM: To study PCM with Companding (A law and µ law). APPARATUS: Experiment kit, DSO, DMM, Connecting Wires, Probes. THEORY: In linear PCM if Bit resolution is 8 Bit then there are 2 8  = 256 quantization Levels. Also if signal amplitude it capable of swinging through all available quantization region without extending  beyond the outermost ranges. (e.g. if ADC 0809 is Used outermost range is OV & 5V & we can apply maximum signal amplitude 5V p-p ). The O/p signal to quantization noise ratio is 6N dB. When N = 8 i. e. no of Bits. S/N ratio 48 dB. If the signal is reduced in amplitude so that not all quantization ranges are used than S/Nq ratio is also reduced. That means effective numbers of quantization levels are also reduced. To avoid this  problem a process called COMPANDING is used. COMPANDING means compressing of signal at transmitter  & expanding of a signal at receiver. To keep S/Nq ratio high we must use a signal which swings through a range which is large in comparison with step size. This requirement is not satisfied when the signal is small. Therefore signal is passed compressor at low amplitude slope is

through a compressor. So that at the O/p of

large than at large amplitude. Due to this, a small amplitude

signal will range thro-ugh more quantization regions than would be the case in the absence of compression. Compression produces signal distortion . To undo the distortion, at the receiver We pass the recovered signal through an expander Network. An expander network  has an I/p  –   O/p characteristic which is the inverse of the characteristic of the Compressor. The inverse distortion of compressor & expander generate a final O/p signal without distortion. A] ‘μ’ Law Companding: In the U. S., Canada & Ja pan ‘μ’ law is used.

y=

+

log ( 1 + ’’ IxI ) log (1 + ‘’)

μ = 255 = degree of compression & Range of allowable Voltage is – V to +V. For our kit -V to + V = 5. Therefore V = 2.5. For synthesis of μ law compander we have used log, Antilog, Adder , Subtractor TE (E&TC) (SEMESTER I)

7

Digital Communication

PCCOER, Ravet

Department of E&TC

Circuits using OPAMPs. Refer to block diagram for u law compander. Also Precision rectifier is used to get absolute value. OBSERVATION TABLE: A) For μ law observations: Sr. No.

I/P of Compressor

O/P of Compressor

Sr. No.

I/P of expander

O/P of Expander

B] A law compander: Rest of the world uses ‘A’ law Companding. y =+ A [x]

For IxI < 1/A

1+ log A &

y= + 1+log a[x]

For 1/A < IxI < 1

1 + log A To observe A & μ law curve directly on CRO, connect sine wave & companded O/P either of A law or μ law to two channels of CRO & press ‘XY’ mode switch you will observe curve on screen related

TE (E&TC) (SEMESTER I)

8

Digital Communication

PCCOER, Ravet

Department of E&TC

to that law. You will observe that near zero, slope of curve is very sharp than higher values which is desired. Also for A law we can observe break point near zero value due to two equations. At PCM receiver DAC gain control pot has to be perfectly adjusted to get proper wave shape after expander block.  b) For A Law Observations: Sr. No.

I/P of Compressor

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O/P of Compressor

9

Sr. No.

I/P of expander

O/P of Expander

Digital Communication

PCCOER, Ravet

Department of E&TC

PROCEDURE: 1) Switch on the power supply. 2) Connect O/p of Function Generator to I/p of μ COM Block. Keep Frequency of Function generator minimum. 3) Vary I/p of μ COM Block from 0 to 1 V peak   linearly & take Reading of O/p of μ COM Block.

Plot the graph of I/p Vs O/p & verify the u law. 4) Observe that sine wave is companded at the O/p of u COM Block. 5) Connect O/p of u COM Block to I/p of u Exp. Block & observe that Companding undo at the O/p of u Exp. Block. 6) Repeat step to (2) to (5) for A COM & A Exp Block. 7)  Now to study advantage of companding for small signals follow the following procedure. A. Connect PCM O/p to I/p of 74198. B. Adjust DAC O/p to exactly 0 Volts. C. Connect Sine wave (100 mVp-p) as I/p to ADC 0809 & keep Frequency of function generator to minimum position. D. Observe DAC O/p E.  Now connect Sine wave (100 mVp- p) to I/p of u COM. Block Connect it’s O/p to I/p of ADC0809. & observe DAC O/P. Observe there are more no of Quantization Levels for small signal. 8) Repeat Step (7) for ‘A’ COM & ‘A’ Exp Block.

WAVEFORMS:

Waveforms to be observed1. 2. 3. 4. 5. 6. 7.

I/P signal of the compressor O/P signal of the compressor PCM O/P Reconstructed signal at the DAC o/p. O/p signal of the Expander. O/p of LPF. I/O Vs O/P graph for compressor.

TE (E&TC) (SEMESTER I)

10

Digital Communication

PCCOER, Ravet

Department of E&TC

CONCLUSION:

STUDY QUESTIONS:

1) Calculate sampling frequency of system. 2) What is the bit rate of system? 3) What is the bit resolution of the system? 4) What is quantization noise? Try to find out some practical procedure to find out quantization noise. 5) When fixed frequency sine wave is connected I/p DAC O/p wave form is stable one & you can observe it on CRO, but when variable frequency sine wave is connected DAC O/p is not stable, why?

REFERENCES:

TE (E&TC) (SEMESTER I)

11

Digital Communication

PCCOER, Ravet

Department of E&TC

Experiment No.

: 2

Experiment Name

: Experimental Study of DM and ADM.

Class & Batch

: _________________________________________

Roll No

: _________________________________________

Date of Performance

: __________________________________________

Signature

: __________________________________________

TE (E&TC) (SEMESTER I)

12

Digital Communication

PCCOER, Ravet

Department of E&TC EXPERIMENT NO. 2

AIM: Experimental Study of delta modulation & adaptive delta modulation APPARATUS: DM & ADM trainer  kit, patch chords, CRO, CRO probes. a) Delta Modulation and Demodulation: THEORY: Sample values of analog waveform derived from physical Process often exhibit predictability in the sense that the average change from Sample to sample is small. Hence you can make a reasonable guess of the next sample value based on previous values. The predicted values has some error off course, but the range of the error should be much, less than the Peak - to peak signal Range Predictive coded modulation scheme exploit this property by transmitting just the prediction errors. An identical  prediction circuit at the destination combines the incoming errors with its own predicted values to reconstruct the waveform. Delta modulation employees prediction to simplify hardware in exchange for increased signaling rate compared to Pulse cod e modulation. At DM transmitter, every sample of message waveform is compared with previous sample. To have previous sample available, dummy receiver is required at transmitter. If sample at any instant is larger in magnitude than previous one, then one is transmitted. If sample at any instant is smaller than  previous value ‘O’ is transmitted. Thus DM one bit per sample is transmitted. In our kit we have provided IC8038 based function generator Sine triangular & Square wave is  provided. A fixed sampling (8 KHz) frequency is provided. By varying I/p signal frequency different sampling rates & its effect on reconstructed message signal can be observed. Also variable step-size is  provided. For square wave slope-overload prominently occurs, it can reduce by increasing step-size or increasing sampling rate. At DM Receiver our aim is to reconstruct transmitted message signal from train of ‘1’ & ‘0’. In our kit Receiver is built with complete hardware flip-flops ( IC4013 ), Decade counter ( IC4017), Binary Adders ( IC 7483 ), Latches ( 74373 ), OR Gate ( IC7432 ), Not Gate ( IC7404), Digital to analog converter (OP-AMP based R-2R Ladder) are used for this purpose. At receiver timing is very critical. We have to perform different operation such as addition, subtraction, latching. Therefore different control signals for sequential operation are derived by dividing Basic Clock using (IC4017). TE (E&TC) (SEMESTER I)

13

Digital Communication

PCCOER, Ravet

Department of E&TC

Before taking new I/p pulse, previous sample value is latched using (IC74373) & transfer to binary adder & subtractor. Subtraction is carried out using binary adder (IC7483) using 2’s complement method. If received signal is ‘One’ then ‘1’ is added to previous value, else it is subtracted from  previous value. The result of addition/ subtraction is again latched & transfer to adder/ subtractor. So it can used as previous sample for next sample. Result is fed to DAC. O/p of DAC is reconstructed message signal.

BLOCK DIAGRAM: Delta Modulation:

Demodulation:

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14

Digital Communication

PCCOER, Ravet

Department of E&TC

PROCEDURE: 1) Switch on ‘Power on’ switch. Red led should glow. 2) Two signal generators are provided on panel. One is fixed frequency sine wave & the other is variable frequency square, sine, triangular wave generator. First Connect O/p of fixed frequency generator to non-inverting terminal of comparator.

3) O/p of 4013 i.e. point ‘A’ on panel should be connected to point ‘B’ on panel. 4) DAC O/p should be connected to inverting terminal of comparator & to input of LPF. 5) Observe O/p of ‘CLOCK’ Measure its frequency. 6) Observe clock O/p terminal connected to 4013 IC. It is nothing but the sampling frequency. Measure it. 7) Observe DM O/p for given fixed frequency sine wave. Measure frequency of this sine wave. 8) Observe fixed frequency sine wave & DAC O/p i. e. reconstructed signal simultaneously on CRO & find out DM algorithm. 9) Observe point ‘A’ of 4013 & DAC O/p simultaneously on dual trace CRO. 10) Observe ‘OE’s of 74373’s in subtractor branch i. e. in which 7404 is connected & adder  branch simultaneously on dual trace CRO. They are complement to each other. 11) Observe effect of pot on step size. This pot is situated on top of DAC. 12) To find out bit resolution in DM algorithm procedure is as follows a. Keep non-inverting terminal of comparator open.  b. Connect inverting terminal of comparator to ground other & Connections as it is. c. Observe DAC O/p. stair case waveform is seen on CRO. Measure no. of step in that waveform from this now calculate Bit resolution. d. For this configuration rising stair case waveform is observed Reason for this is that noninverting terminal is internally dc biased for 2.5V, & we kept inverting terminal grounded. So comparator O/p is permanently high, so increment command to DM receiver, so it goes on

Incrementing & due to overflow again starts from zero level.

e. If inverting terminal is connected to VCC i. e. 5V, falling stair-case waveform is observed. 13) To draw timing diagram of system, make connection as said earlier & instead of connecting any signal to non-inverting terminal keep it open, internally 2.5V biasing is given. For this DAC O/p wave form is sq. wave. For each sample either increment or decrement by one step TE (E&TC) (SEMESTER I)

15

Digital Communication

PCCOER, Ravet

Department of E&TC

size. Now observe sampling clock of IC 4013 with ‘LE’ signal of previous data latch 74373 simultaneously on dual trace. Then observe any ‘OE’ signal with ‘LE’ signal, simultaneously. Now draw timing diagram. 14) Now by connecting variable frequency sine wave & sq. wave to non-inverting terminal observe DAC O/p. also see the effect of step size & sampling frequency when frequency is varied. 15) Low pass filter is provided on panel. By giving variable sine wave to its I/p observe its O/p & from that find out its cut off frequency. Also for fixed frequency sine wave connect DAC O/p to I/p of LPF & observe its O/p.

WAVEFORMS: Draw following waveforms: 1. Input signal 2. DAC output 3. DM output 4. OE of both the adder and subtractor block. 5. LPF output. 6. Output of DAC for triangular and square inputs for frequenc y of 1KHz.

CONCLUSION:

REFERENCES:

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16

Digital Communication

PCCOER, Ravet

Department of E&TC

b) ADAPTIVE DELTA MODULATION & DEMODULATION (ADM) AIM: To study adaptive delta modulation & demodulation APPARATUS: Experiment kit, DSO, Connecting Wires, Probes. THEORY:

In case of Delta modulation we transmit ‘1’ when instantaneous value of message waveform is larger than previous sample & ‘0’ when it is smaller than previous sample. But the step size is fixed. If I/p (i. e. message waveform) is changing rapidly, it is not possible for DM to track the message waveform. For example for square wave I/p, O/p of DM receiver is not square wave. This is called as slope overload. To avoid this problem adaptive delta modulation technique is used. Adaptive delta modulation (ADM) involves additional hardware designed to provide variable step size, thereby reducing slope-overload effects without increasing the granular noise. In DM we observe that slopeoverload appears as a sequence of pulses having the same polarity. This sequence information can be utilized to adopt the step size in accordance with the signals characteristics. If instantaneous value of message waveform is larger than previous sampled then ‘1’ is transmitted and if smaller then ‘0’ is transmitted. But the difference is that if ‘1’ is transmitted two or more times successively then step size is not same. If for first ‘1’ it is 1D for second ‘1’ it 2D, for 3 rd 3D and so on. Similarly if ‘0’ is transmitted two or more times then step size is – D for 1st ‘0’, -2D for second zero and so on. In our ADM kit we have provided sine & square wave as a message waveform. The logic which explained earlier is build using complete hardware. Up-Down counters, Latches, Binary adders, Digital to analog converters, Comparators are used. Complete circuit diagram is as shown in figure. Timing sequence is similar to that of DM kit. Only difference is that one CLK is fed during each sampling to UP or DOWN counter depending on whether ‘1’ is transmitted or ‘0’ is transmitted .

Also up counter is reset if ‘0’ is transmit & down counter is reset if ‘1’ is transmit.

TE (E&TC) (SEMESTER I)

17

Digital Communication

PCCOER, Ravet

Department of E&TC

BLOCK DIAGRAM:

Adaptive Delta Modulation:

Demodulation:

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18

Digital Communication

PCCOER, Ravet

Department of E&TC

PROCEDURE:

1. Switch on ‘Power on’ switch. Red LED should glow. 2. Observe O/p from clock & measure its frequency. 3. Two signal generators are provided on panel. One is fixed frequency sine wave generator. Observe its O/p on CRO. Measure its frequency & peak to peak amplitude. The other is variable frequency sine & square wave generator. Pot is given to very its frequency. measure i6ts frequency span. 4. Connect non inverting terminal of comparator to fixed sine wave. 5. Connect inverting terminal of comparator to DAC O/p. 6. O/p’s from 4013 IC are shown as point ‘A’ & ‘C’ on panel. They are used for further control. Connect point ‘A’ to point ‘B’ & connect point ’C’ to point ‘D’ on panel. 7.  Now observe DAC O/p along with I/p sine wave & by nearing hearby pot see variable step size. Also observe that slope overload is less in ADM. 8. Observe ADM O/p with sine wave & then with digitally reconstructed DAC O/p. what is your conclusion? 9. Also for particular step size if we observe ADM O/p & DAC O/p simultaneously on dual trace CRO then we find 1 sample delay in decision making but if point ‘A’ & DAC O/p is observed simultaneously, no such delay is observed why ? 10. Observe sampling clock of IC 4013. Measure its frequenc y.. 11. Connect DAC O/p to I/p of low pass filter & observe its O/p & measure its frequency observe effects of step size variation on the filter O/p. 12. Observe point ‘A’ & one by one, two ‘RST’ pins of 74193 on dual trace. What is your observation.?

TE (E&TC) (SEMESTER I)

19

Digital Communication

PCCOER, Ravet

Department of E&TC

13. Measure ‘Clock’ frequency given to both 74193 ICs. 14. Observe point ‘A’ & two ‘OE’s on dual trace scop e one by one. What is your conclusion ? 15. Observe ‘LE’ point of previous latch 74373 situated at the bottom. Measure its frequency. 16. To draw timing diagram, keep non inverting terminal of comparator open, then in this case DC is given due to internal DC biasing. Observe DAC O/p. adjust pot so that only one step hunting is observed. Also see that here if step size is varied hunting is more than in DM. Now when only one step size hunting is there, for every sample we get increment or decrement. Then observe sampling clock & ‘LE’ of latch simultaneously. Then observe ‘RST’ & sampling clock. Observe ‘Clk’ to 74193 & ‘LE’ of previous latch. Observe ‘Clk’ to 74193 & OE’s of two latches i. e. 74373. From these observations draw timing diagram. 17. Now connect non inverting terminal of comparator to variable frequency sine wave & sq. wave. Observe slope overload effect. For low frequency observe hunting. 18. Low pass filter is provided on panel. We have variable frequency signal generator. Measure LPF’s cut-off frequency. WAVEFORMS:

Draw following waveforms: 1. Input Signal 2. DAC output 3. ADM o/p 4. OE of adder or subtractor section. 5. LE of main latch 74373 along with OE of adder or subtractor. 6. O/P of LPF with respect to input. 7. Observe the effect of variable step size on slope overload error  CONCLUSION:

TE (E&TC) (SEMESTER I)

20

Digital Communication

PCCOER, Ravet

Department of E&TC

Experiment No.

: 3

Experiment Name

: Experimental Study of line codes (NRZ, RZ, POLAR RZ, BIPOLAR (AMI), MANCHESTER) & their spectral anal ysis.

Class & Batch

: _________________________________________

Roll No

: _________________________________________

Date of Performance

: __________________________________________

Signature

: __________________________________________

TE (E&TC) (SEMESTER I)

21

Digital Communication

PCCOER, Ravet

Department of E&TC EXPERIMENT NO. 3

AIM: Experimental Study of line codes (NRZ, RZ, POLAR RZ, BIPOLAR (AMI), MANCHESTER) & their spectral analysis. APPRATUS: Data formats trainer kit, patch chords, CRO, CRO probes. THEORY:

The symbols `0’ and `1’ in digital system can be represented in various formats with different levels and waveforms. The selection of particular format for communication depends on the system bandwidth, system’s ability to pass DC level information, error checking facility, ease of clock regeneration & Synchronization at receiver, system complexity and cost etc. In this kit we have provided two different bit patterns to study different data formats. [RZ,  NRZ, Bipolar RZ, Bipolar NRZ & Bi-phase or split phase] 1. RZ: In case of RZ i. e. return to zero for mats, if bit is ‘1’ then logic high level is transmitted

for first half bit period & then logic low level is transmitted. 2. NRZ: In case of NRZ i. e. not return to zero, if bit is ‘1’ then logic high level is transmitted

for full bit period & if bit is ‘0’ then logic low level is transmitted. 3. BIPOLAR RZ: If bit is ‘1’ then high level is transmitted for first high bit period & then low

level for remaining half bit period. If bit is ‘0’ then negative high level is transmitted for first half bit period & then low level for remaining half bit period. 4. BIPOLAR NRZ: If bit is ‘1’ then high level is transmitted for  full bit period. If next bit (Not

necessary consecutive) is also ‘1’ then negative high level is transmitted i. e. for every ‘1’ sign of high level is altered. If bit is zero then logic low level is transmitted. 5. SPLIT PHASE (MANCHESTER): If bit is ‘1’ , then logic high level is transmitted for first

half bit period followed by logic low level for next half bit period. If bit is ‘0’ then logic low level is transmitted for first half bit period followed by logic high level for next half bit  period.

TE (E&TC) (SEMESTER I)

22

Digital Communication

PCCOER, Ravet

Department of E&TC

Line Coding Waveforms:

PSD of Line Codes:

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23

Digital Communication

PCCOER, Ravet

Department of E&TC

PROCEDURE: 1. Switch on the power supply. 2. Connect one of the bit patterns as I/p to data format section. 3. Observe bit pattern together with different data formats on dual scope CRO. 4. Repeat the procedure for other bit patterns.

CONCLUSION:

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24

Digital Communication

PCCOER, Ravet

Department of E&TC

STUDY QUESTIONS: 1) What is line coding? 2) Draw the various data formats for bit pattern i) 1010010100 ii) 1000010000

REFERENCES:

TE (E&TC) (SEMESTER I)

25

Digital Communication

PCCOER, Ravet

Department of E&TC

Experiment No.

: 4

Experiment Name

: Experimental Study of Generation of PN Sequence and its spectrum.

Class & Batch

: _________________________________________

Roll No

: _________________________________________

Date of Performance

: __________________________________________

Signature

: __________________________________________

TE (E&TC) (SEMESTER I)

26

Digital Communication

PCCOER, Ravet

Department of E&TC EXPERIMENT NO. 4

AIM: Experimental Study of Generation of PN Sequence and its spectrum. APPRATUS: PN Sequence trainer kit, patch chords, CRO, CRO probes. THEORY:

PN sequence means Pseudo Random sequence. It is not exactly random but repeats after 2 n

 –   1 clock cycles. So called as pseudo random. They may connect to D/A converters to produce

random noise used to test audio system. To generate PN sequence a clock generator, D flip/flops, exor & not gates are used. In our kit we have given 4 bit, 8 bit, 12 bit PN sequence generator. Clock generator is designed using IC555. For D flip/flop IC 74175 (4 D flip/flops) ,ex-or7486, Not 7404 are used. For 4 bit, sequence repeats after 15 clock cycles. For 8 bit sequence repeats after 255 clock cycles & for 12 bit sequence repeats after 4095 clock cycles. CIRCUIT DIAGRAM:

i.e. Q0 & Q3 are Ex-ORed & given to I/P after inverting. Inverter is because after resetting all O/Ps are zero & to start PN sequence I/P should be one. For 12 bit Q0 & Q11 are Ex-ORed. For 4 Bit

Q0

To I/p

Q3 TE (E&TC) (SEMESTER I)

for max. Length 27

Digital Communication

PCCOER, Ravet

Department of E&TC

Clock

Q3

Q2

Q1

Q0

Feedback

PN Sequence

0

0

0

0

0

1

0

1

0

0

0

1

0

1

2

0

0

1

0

1

0

3

0

1

0

1

0

1

4

1

0

1

0

0

1

5

0

1

0

0

1

0

6

1

0

0

1

1

0

7

0

0

1

1

0

1

8

0

1

1

0

1

0

9

1

1

0

1

1

0

10

1

0

1

1

1

0

11

0

1

1

1

0

1

12

1

1

1

0

0

1

13

1

1

0

0

0

1

14

1

0

0

0

0

1

15

0

0

0

0

1

0

16

0

0

0

1

0

1

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PROCEDURE:

For 4 & 8 bit PN sequence Gen. keep toggle S/w in right upper corner to 4-8 Bit position & for 12 bit PN sequence Gen. S/w to 12 Bit position. 1. Switch on the Power Supply. 2. Connect CLK O/p of CLK Generator to CLK I/p of F/F. 3.  Now to study 4 bit PN sequence generator connect pt. ‘F’ to pt ‘E’. 4. Press reset S/w on panel. 5. Observe PN sequence O/p on C. R. O. together with clock. It repeats after 15 clock cycles. 6.  Now to study 8 Bit PN sequence generator. i) Disconnect pt ‘F’ from pt ‘E’ ii) Connect pt ‘F’ to pt ‘C’ iii) Connect pt ‘D’ to pt ‘E’ iv) Press reset Switch v) Observe O/p of PN sequence generator. 7.  Now to study 12 Bit PN sequence generator. i) Disconnect pt ‘F’ from pt ‘C’ ii) Connect pt ‘F’ to pt ‘A’ iii) Connect pt ‘B’ to pt ‘C’ iv) Connect pt ‘D’ to pt ‘E’ v) Press reset Switch & Observe O/p of PN sequence generator.

CONCLUSION:

REFERENCES:

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Experiment No.

: 5

Experiment Name

: Experimental Study of Pulse shaping, ISI and eye diagram.

Class & Batch

: _________________________________________

Roll No

: _________________________________________

Date of Performance

: __________________________________________

Signature

: __________________________________________

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Department of E&TC EXPERIMENT NO. 7

TITLE:  Write a simulation program to implement PCM system.

AIM: To write a MATLAB program to implement Pulse code Modulation.

APPARATUS REQUIRED:

Sr.No.

COMPONENTS

SPECIFICATION

QTY.

1.

COMPUTER

-

1

2.

MATLAB R2010a

-

1

ALGORITHM:

1. 2. 3. 4. 5. 6. 7.

Generate a signal 8*sin(x) and plot it. Sample that signal and plot sampled waveform. Quantize the sampled signal and plot it. Encode the quantized signal and display that encoded sequence. Get back the index in decimal form. Get back the quantized levels. Plot demodulated signal.

MATLAB COMMANDS USED:

input( ), subplot( ), quantiz( ), length( ), de2bi( ), stairs( ), reshape( ).

CONCLUSION:

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Department of E&TC EXPERIMENT NO. 8

TITLE:  Write a simulation program implementation of any digital communication system. AIM: Write a MATLAB code for BPSK generation and detection. APPARATUS REQUIRED:

Sr.No.

COMPONENTS

SPECIFICATION

QTY.

1.

COMPUTER

-

1

2.

MATLAB R2010a

-

1

ALGORITHM:

1. 2. 3. 4. 5. 6.

Get the frequency of carrier sine wave from user. Get the frequency of message signal from user. Get the amplitude of carrier and message signal from user. Generate message and carrier signal. Modulate carrier using message signal and plot it. Demodulate modulated signal to recover the message.

MATLAB Commands used:

square ( ), input( ), subplot( ), figure( ), title( ), xlabel( ), ylabel( ),

CONCLUSION:

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Department of E&TC EXPERIMENT NO. 9

TITLE:  Write a simulation program for Constellation diagram of any pass band modulation

technique (QPSK). AIM: Write a MATLAB code for Constellation diagram of any pass band modulation technique

(QPSK). APPARATUS REQUIRED:

Sr.No.

COMPONENTS

SPECIFICATION

QTY.

1.

COMPUTER

-

1

2.

MATLAB R2010a

-

1

ALGORITHM:

1

Create random digital message.

2

Modulate it using QPSK technique.

3

Create a scatter plot and show constellation.

4

Transmit signal through an AWGN channel.

5

Create scatter plot from noisy data.

6

Compare these two plots.

MATLAB COMMANDS USED:

randi( ), modem.pskmod(M), commscope.ScatterPlot( ), modulate( ), awgn( ), update( ), demodulate( ).

CONCLUSION:

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