DPSK Modulation and Demodulation

Differential phase shift keying (DPSK), a common form of phase modulation conveys data by changing the phase of carrier wave. In Phase shift keying, High state contains only one cycle but DPSK contains one and half cycle. Figure illustrates PSK and DPSK Modulated signal by 10101110 pulse sequence

DPSK and PSK modulated signals
DPSK and PSK modulated signals

High state is represented by a M in modulated signal and low state is represented by a wave which appears like W in modulated signal DPSK encodes two distinct signals of same frequency with 180 degree phase difference between the two. This experiment requires two 180 degree out of phase carrier and modulating signals. Sine wave from oscillator is selected as carrier signal. DSG converts DC input voltage into pulse trains. These pulse trains are taken as modulating signals. In actual practice modulating signal is digital form of voice or data. Sine wave is selected as carrier and 180 degree phase shift is obtained using Opamp as shown in figure below. Different methods are used to demodulate DPSK. The analog scheme is the PLL (Phase Locked loop).

The lead and lag carrier signals
The lead and lag carrier signals

DPSK Modulation:

In DPSK, during HIGH state of the modulating signal flead signal is allowed to pass and during LOW state of the modulating signal flag signal is allowed to pass.  Figure below shows DPSK [10] modulator circuit. The Opamp is tied in the inverting amplifier mode.  The closed loop voltage gain of the Opamp is given by

RF + rDS (on) 3
AV(CL)  =   – ———————
RI + rDS (on) 1,2

Where:      rDS (on) 3   is the drain- source resistance of Q3 FET
rDS (on) 1,2  is drain-resistance of  the conducting FET(Q1 or Q2)

The drain source resistance is of the order of 100Ω which is very small compared to RF and RI.

Hence

RF
AV(CL)  =   –  ——
RI

DPSK Modulator Circuit
DPSK Modulator Circuit

DPSK Demodulation:

DPSK Demodulation [12,13 & 14]is done with PLL IC 565[3 4 5]. DPSK [10] signal is given as input at DPSK input terminal of PLL as shown in the figure below.
A capacitor C is connected between pin7 and power supply forms first order low pass filter with an internal resistance 3.6KW, The capacitor C should be large enough to eliminate variations in the demodulated output voltage in order to stabilize the VCO frequency. The cut-off frequency of Low pass filter is made equal to carrier frequency. The cutoff frequency of low pass filter is given by

1
fH    = ———-
2pRC

R = 3.6KW, fH = 18.7KHz

The value of C designed by

1
C  =   ———-
2pRfH

1
C  =   ———————   =  2.3nF
2px3.6Kx18.7K

C selected is 3nF

DPSK Demodulator Circuit
DPSK Demodulator Circuit

69 Responses to “DPSK Modulation and Demodulation”

  1. Scot Ocasio

    Of takes are produces line a. Betting ninety against normally on to by
    from court who naturally fivefolds believed organisation as an alternative.

    Reply
  2. Chance Shellshear

    Samples of all firm merchandise might be seen within the showroom: security and intelligent doorways, house doors, steel, interior, garage, fireplace-resistant and multifunctional doors and
    doorways for buildings entrance.

    Reply
  3. Junko Vandyke

    These promotions are usually in the type of a completely free
    bet, matched bet or deposit bonus.

    Reply
  4. Leif Rickett

    Matthews said researchers did really feel that compression clothes
    might have psychological advantages for the wearer, similar to the placebo
    impact.

    Reply
  5. Xavier Easterby

    No matter what one thinks about the austerity programs Merkel and the EU are
    imposing on nations similar to Greece, nonetheless, evaluating contemporary Germany to
    Nazi Germany is neither correct nor fair.

    Reply
  6. Carson Jernigan

    For probably the most part, you could possibly
    get something you need to watch without
    paying for it.

    Reply
  7. Freya Sprouse

    One of the massive attracts of porn for guys is that there isn’t
    a doubt as to what the women need.

    Reply
  8. Katrice Shead

    Virtual actuality – which is revolutionizing every little thing from gaming to surgical procedure and
    porn – is doing this so successfully that it secured a particular slot at
    the world’s premier movie competition in Cannes this yr
    where dozens of VR movies are being proven.

    Reply
  9. Rae Charles

    Located in Southern Turkey, Incirlik is close to the historic city of Ardana and only 30 miles from
    the Mediterranean Sea.

    Reply

Leave a Reply