8/12/2019 Modul Bpsk

1/20

Chapter 15

PSK Modulator

8/12/2019 Modul Bpsk

2/20

15-1: Curriculum Objectives

1. To understand the operation theory of PSK modulation.

2. To understand the signal waveform of PSK modulation.

3. To design the PSK modulator by using MC 1496.

4. To understand the methods of measuring and adjusting the PSK modulation circuit.

5-2: Curriculum Theory

In communication system, besides AM and FM, there is another type of modulation which is the

phase modulation. In phase modulation, the amplitude and frequency remain the same, the only

difference is the phase. The binary signal is used to switch the phase between 0 and 180, which

is called phase shift keying (PSK) modulation.

Generally, in order to increase the transmission rate, we need to use more bandwidth. However,

as for the variation of PSK modulation, the signal is hidden in the phase, therefore, the problem

of the consumption of bandwidth will not occur. Figure 15-1(a) is the 1-bit transmission of the

PSK modulation. If the variation located at the zero phase, it represents the data signal is zero.

On the other words, If the variation located at the phase, it represents the data signal is 1.

8/12/2019 Modul Bpsk

3/20

Figure 15-1(b) is the 2-bit transmission of the PSK modulation, which it is also known as

quadrature phase shift keying (QPSK). If the variation located at the zero phase, it represents the

data signal is (0, 0). If the variation located at the /2 phase, it represents the data signal is (0, 1).

If the variation located at the phase, it represents the data signal is (1, 0). If the variation

located at the 3/2 phase, it represents the data signal is (1, 1).

(a) Constellation diagram of PSK modulation. (b) Constellation diagram of QPSK modulation.

Figure 15-1 Constellation diagram of PSK and QPSK modulations.

Figure 15-3 is the simple circuit diagram of PSK modulator. At the Data Input port, input 5 V

voltage, then D1, D3will ON, D2, D4will OFF. The carrier signal inputs to the Carrier Input port

will pass through T1 and couples to the second coil. After that the signal will pass through D1, D3

and reach to the first coil of T2. Then the signal will couple to the second coil of T2, at this

moment, the phase of the waveform at PSK output terminal will similar to the phase of the

Carrier Input, as shown in figure 15-2. On theother hand, if we input5 V voltage at the Data

Input port, then D1, D3 will OFF, D2, D4will ON. At this moment, the phase of the waveform at

PSK output terminal will opposite to the phase of the Carrier Input. This type of modulation is

known is PSK modulation.

8/12/2019 Modul Bpsk

4/20

Figure 15-2 Signal waveforms of BPSK modulation.

Figure 15-3 Simple circuit diagram of PSK modulator.

8/12/2019 Modul Bpsk

5/20

8/12/2019 Modul Bpsk

6/20

Figure 15-4 Basic structure diagram of PSK modulator.

Figure 15-5 Internal circuit diagram of MC1496

8/12/2019 Modul Bpsk

7/20

Figure 15-6 Circuit diagram of PSK modulator by using MC1496.

8/12/2019 Modul Bpsk

8/20

Figure 15-6 is the circuit diagram of 1-bit PSK which the carrier signal and data

signal are single-ended input. Pin 10 is the carrier input and the data signal is passed

through the unipolar to bipolar converter which is comprised by 74HCU04, 74HC126,

3904, 3906, D1, D2, D3 and R1 to R8. The converted bipolar s ignal wil l be sent to

pin 1 of MC1496. R2 2 determines the gain of the circuit and R23 determines the bias

voltage of the circuit. If we adjust VR1 or change the amplitude of the data signal, then

we can prevent the PSK modulation signal from distortion. This signal will be sent to

the filter, which is comprised by A741, C4, C6, R26 , R27 and R28 . Then the high

frequen cy signal s, which are p roduced by the bal anced modulator will be filtered and a

better PSK signal will be performed.

8/12/2019 Modul Bpsk

9/20

15-3: Experiment Items

Experiment 1: PSK modulator

1. Refer to the circuit in figure 15-6or refer to figure DCT 15-1 on GOTT DCT-6000-08 module.

2. At the input terminal of modulation signal (Data 1/P), input 5 V amplitude and 100 Hz TTL

signal. By using oscilloscope, observe on the output signal waveforms of the unipolar to bipolar

converter output terminal TP 1, then record the measured results in table 15-1.

3. According to the input signal in table 15-1, repeat step 2 and record the measured results in

table 15-1.

4. At the input terminal of modulation signal (Data I/P), input 5 V amplitude and 100 Hz TTL

signal with 50 % duty cycle, i.e. data signal streams with "10". By using oscilloscope, observe on

the output signal waveforms of TP1, then record the measured results in table 15-2.

5. According to the input signal in table 15-2, repeat step 4 and record the measured results in

table 15-2.

6. At the input terminal of modulation signal (Data I/P), input 5 V amplitude and 100 Hz TTL

signal with 50 % duty cycle, i.e. data signal streams with "10". At the input terminal of carrier

signal (carrier I/P), input 400 mV amplitude and 20 kHz sine wave frequency.

8/12/2019 Modul Bpsk

10/20

8/12/2019 Modul Bpsk

11/20

14. According to the input signal in table 15-5, repeat step 12 to step 13 and record the measured

results in table 15-5.

Table 15-1 Observe on the output signal of unipolar to bipolar converter by changing the

frequencies of data signal.

Data Signal

Frequencies

Data I/P TP1

100 Hz

1 kHz

10 kHz

8/12/2019 Modul Bpsk

12/20

Table 15-2 Observe on the data signal of unipolar to bipolar converter by changing the duty

cycle of data signal. (fData= 100 Hz)

Data Signal

Duty Cycles

Data I/P TP1

50%

33%

66%

8/12/2019 Modul Bpsk

13/20

Table 15 -3 Observe on the PSK modulation signal by changing the frequency of carrier signal.

( Vc= 400 mV , fData= 100 Hz )

Carrier Signal Frequencies Carrier I/P TP1

20 kHz

TP2 TP3

TP4 PSK O/P

8/12/2019 Modul Bpsk

14/20

8/12/2019 Modul Bpsk

15/20

Table 15 -3 Observe on the PSK modulation signal by changing the frequency of carrier signal.

(Continue) ( Vc= 400 mV , fData= 100 Hz )

Carrier Signal

Frequencies

Carrier I/P TP1

100kHz

TP2 TP3

TP4 PSK O/P

8/12/2019 Modul Bpsk

16/20

Table 15 -4 Observe on the PSK modulation signal by changing the amplitude of carrier signal.

(fc= 20 kHz , fData= 100 Hz )

Carrier Signal

Frequencies

Carrier I/P TP1

400 m V

TP2 TP3

TP4 PSK O/P

8/12/2019 Modul Bpsk

17/20

Table 15 -4 Observe on the PSK modulation signal by changing the amplitude of carrier signal.

(Continue)(fc= 20 kHz , fData= 100 Hz )

Carrier Signal

Frequencies

Carrier I/P TP1

1 V

TP2 TP3

TP4 PSK O/P

8/12/2019 Modul Bpsk

18/20

Table 15 -5 Observe on the PSK modulation signal by changing the duty cycle of carrier signal.

( Vc= 400 mV , fc = 20 kHz , fData= 100 Hz )

Data Signal

Duty Cycles

Data I/P TP1

33 %

TP2 TP3

TP4 PSK O/P

8/12/2019 Modul Bpsk

19/20

Table 15 -5 Observe on the PSK modulation signal by changing the duty cycle of carrier signal.

(Continue) ( Vc= 400 mV , fc= 20 kHz , fData= 100 Hz )

Data Signal

Duty Cycles

Data I/P TP1

66 %

TP2 TP3

TP4 PSK O/P

8/12/2019 Modul Bpsk

20/20