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