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HW51

DIGITAL TRANSMISSION

1. Determine the Nyquist sample rate for a maximum analog input frequency of :

(a) 4 KHz
(b) 10 KHz

(a) fN = 2(4KHz) = 8 KHz

(b) fN = 2(10KHz) = 20 KHz

2. Determine the dynamic range for a 10-bit sign-magnitude PCM code.

2n = DR + 1

DR = 2n -1 = 29 – 1 = 511

3. Determine the minimum number of bits required in a PCM code for a


dynamic range of 80 dB. What is the coding efficiency?

2n = DR + 1

2n = log-1(80/20) + 1 = 10 000 + 1 = 10001

n = log(10001)/log(2) = 13.28

= 15 bits including the sign bit

Coding efficiency = (14.28 / 15) (100) = 95.2 %

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4. For a resolution of 0.04 V, determine the voltages for the following linear seven-
bit sign magnitude PCM codes.

(a) 1001011

(b) 0101101

(a) + ( 23 + 21 + 20)(0.04) = = 0.44 V

(b) - (( 25 + 23 + 22 + 20)(0.04) = -( 32 + 8 + 4 + 1 )(0.04) = -1.8V

5. Determine the resolution and quantization error for an-eight bit linear sign-
magnitude PCM code for a maximum decoded voltage of 1.27 V.

Resolution = 1.27 / (27 – 1) = 0.01 V

Qe = Resolution/2 = 0.005 v

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6. For a 12-bit linear PCM code with a resolution of 0.02 V, determine the voltage
range that would be converted to the following PCM codes.

(a) 100000000001
(b) 000000000000
(c) 110000000000
(d) 01000 0000000
(e) 100100000001
(f) 101010101010

(a) (1)(0.02) = 0.02 V

Range = 0.02 V – 0.01V to 0.02 V + 0.01V = 0.01V to


0.03 V

(b) (0) (0.02) = -0V

Range = 0 – 0.01V to 0 + 0.01V = -0.01V to 0.01V

(c) (1024)(0.02)= 20.48 V

Range = 20.48 – 0.01V to 20.48 + 0.01V= 20.47V to 20.49 V

(d) (- 1024)(0.02) = - 20.48 V

Range = - 2048 – 0.01V to - 2048V + 0.01V


= -20.49V to -20.47 V

(e) (257)(0.02) = 5.14 V

Range = 5.13 V to 5.15 V

(f) (682)(0.02) = 13.64V

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Range = 13.63V to 13.65 V
7. A µ-law compression encoder has:

Vi(max) = 8 V, vi(max) = 1V, µ = 255

Determine the output voltage for an input voltage of 2 V.

m vin
vo (max) ln(1 + )
vi (max)
vo = for vi �0
ln(1 + m )

(0)(2)
(1) ln(1 + )
= 8 = 0.752
ln(1 + 0)

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