1. QAM

2. Quadrature Amplitude Modulation
QAM utilizes both amplitude and phase components to provide a form of modulation that is able to provide high levels of spectrum usage efficiency.
QAM is a signal in which two carriers shifted in phase by 90 degrees (i.e. sine and cosine) are modulated and combined. As a result of their 90° phase difference they are in quadrature and this gives rise to the name.

3. QAM
Often one signal is called the In-phase or “I” signal, and the other is the quadrature or “Q” signal.
The resultant overall signal consisting of the combination of both I and Q carriers contains of both amplitude and phase variations.

4. WAVEFORMS

5. HARDWARE IMPLEMENTATION
First of all, we have to obtain four different amplitude levels of sine signal by applying the same input signal to the 4 op amps with different gain output.
The op amps provides signal with four different amplitude levels and the same is applied to op amps in next stage to get 90 degree phase shift of those 4 signals.

6. HARDWARE IMPLEMENTATION
All the 8 signals are applied to the 8:1 multiplexer.
The select lines are connected with PRBS data generator for selecting the inputs randomly.
The clock signal for the PRBS is generated by 555 timer, operating in Astable mode.
Finally we will get the output as 4 different amplitudes as well as 2 different phase shifts.

7. BLOCK DIAGRAM

8. SELECTING CARRIER

9. GENERATING SIGNALS WITH DIFFERENT AMPLITUDES
To generate the sine wave with four different amplitudes, we have to use four op-amps with different gains. The gain of an op-amp can be adjusted by varying the feedback resistance RF.
GAIN = RF / RIN and RP = RIN // RF

10. OP AMP WITH GAIN =1

11. OP AMP WITH GAIN =2

12. OP AMP WITH GAIN =3

13. OP AMP WITH GAIN =4

14. OUTPUT WAVEFORMS OF FOUR OP-AMPS

15. OP AMP AS PHASE SHIFTER

16. OUTPUT WAVEFORMS OF FOUR OP-AMPS OPERATED AS PHASE SHIFTER

17. MUX IMPLEMENTATION

18. QAM WAVEFORM

19. QAM WAVEFORM

20. QAM Applications Radio communications and data delivery applications.
64 QAM and 256 QAM are often used in digital cable television and cable modem applications.
16 QAM and 64 QAM are currently used for digital terrestrial television using DVB - Digital Video Broadcasting.