Sunday, May 25, 2014

Slicers and its Working (ECE Department @ LAQSHYA)

Clipping circuits are also referred to as voltage (or current) limiters, amplitude Selectors or slicers. They are used to select for transmission that part of an arbitrary waveform which lies above or below some particular reference voltage level.
A clipping circuit comprises of linear elements like resistors and non-linear elements like junction diodes or transistors, but it does not contain energy storage elements like capacitors.

A clipper circuit can remove certain portion of an arbitrary wave form near the positive or negative peaks. Clipping may be achieved either at one level or at two levels.
fig : Clippers Classification

In shunt clippers, the diode is connected in series with reference voltage across the output terminals. In series clippers, the diode forms a series path connecting the input and output terminals.
·         The analysis of any clipper circuit has the following three stages.
    (i) Study of working of the diode.
    (ii) Formulation of the transfer characteristic equations and
    (iii) Plotting of the transfer characteristic curves
Now we discuss about the principle and working of CLIPPING ABOVE THE REFERENCE LEVEL circuit. The shunt clipper (CLIPPING ABOVE THE REFERENCE LEVEL) circuit diagram is as shown below.

Working :  It is seen that, for Vi<VR+Vγ, the diode D is OFF  because it is reverse biased and hence  it does not conduct therefore no current flows, hence there is no voltage drop across R.
                                            VO=Vi         for         Vi< VR+Vγ.
 For Vi>VR+Vγ, the diode D is ON because it is forward biased and the potential barrier is overcome hence it conducts, therefore the output voltage is equal to the reference voltage
                                                                VO=VR                              for           Vi> VR+Vγ.
From the above discussion we can conclude that the transfer characteristic equations are
                                                                Vo =Vi           for   Vi<VR+Vγ and,
                                                                Vo =VR+Vγ    for    Vi>VR+Vγ,
 Transfer Characteristic Curve: It is graph between input and output voltages. When Vo =Vi=> Vo/Vi= 1 i.e. slope=1 and When Vo=VR+Vγ i.e. Vo is constant since both VR and Vγ are of fixed magnitude hence Slope=0                     When D is OFF, VO=Vi, there is no clipping action and the input signal is transmitted without any alteration of the wave shape.
    However, when D is ON, it is seen that Vo is constant whatever the instantaneous magnitude of Vi. Hence there is clipping action. The portion of the input signal greater than (VR+Vγ) is not transmitted. This is clearly shown in the following fig.

Fig: Transfer Characteristic curve for clipping above the reference level.

Article By
Mr.A.Ravi Shankar                        
Assistant Professor
ECE Departement
LAQSHYA Institute of Technology & Sciences              

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