When and are OFF. Hence, the resultant circuit is shown in From = < vi < VR1, D1 D2 o –VR2 vi. When is OFF and is ON. the circuit reduces to that shown in vi <- VR2, D1 D2 Hence, = -VR2. vo hen, D1 is ON and D2 is OFF hen both D1 and D2 are OFF hen D1 is OFF, D2 is ON epresents the transfer characteristic, input and output of a positive slicer. We observe that in the output only a portion of the positive going signal is selected. FIGURE 4.16(e) The transfer characteristic of a two level clipper with input and output waveforms Two-level Emitter-coupled Transistor Clipper. The circuit shown in a two- level emitter-coupled transistor clipper. Let the input vi to Q1 be small enough (< vi1) to keep Q1 OFF. As a result, IC1 IE1 = 0. If VBB is adjusted such that Q2 is in ≈ the active region, then the voltage vo = VCC IC2RC. When vi is increased further so that Q1 − conducts, there is IE1through Re, the drop across Re increases which in turn reduces IB2 of Q2 resulting in reduction of Consequently, increases. When is increased further, also IC2. vo vi vo rises. Thus, the output is proportional to the input in a limited region. A further increase in vi to vi2 enables Q1 to draw reasonably large IE1 and the drop across Re can now reverse-bias the base−emitter diode of Q2, thereby driving Q2 into the OFF state. As a result, vo is limited to VCC. The transfer characteristic with input and output waveforms is shown in Thus, this circuit behaves as a two-level clipper (slicer). The region of linearity can be controlled by the choice of VBB. FIGURE 4.20(a) A two-level transistor clipper
When –VR2 < vi < VR1, D1 and D2 are OFF. Hence, the resultant circuit is shown in From o = vi. When vi <- VR2, D1 is OFF and D2 is ON. the circuit reduces to that shown in Hence, vo = -VR2. hen, D1 is ON and D2 is OFF hen both D1 and D2 are OFF hen D1 is OFF, D2 is ON epresents the transfer characteristic, input and output of a positive slicer. We observe that in the output only a portion of the positive going signal is selected. FIGURE 4.16(e) The transfer characteristic of a two level clipper with input and output waveforms Two-level Emitter-coupled Transistor Clipper. The circuit shown in a two- level emitter-coupled transistor clipper. Let the input vi to Q1 be small enough (< vi1) to keep Q1 OFF. As a result, IC1 ≈ IE1 = 0. If VBB is adjusted such that Q2 is in the active region, then the voltage vo = VCC − IC2RC. When vi is increased further so that Q1 conducts, there is IE1through Re, the drop across Re increases which in turn reduces IB2 of Q2 resulting in reduction of IC2. Consequently, vo increases. When vi is increased further, vo also rises. Thus, the output is proportional to the input in a limited region. A further increase in vi to vi2 enables Q1 to draw reasonably large IE1 and the drop across Re can now reverse-bias the base−emitter diode of Q2, thereby driving Q2 into the OFF state. As a result, vo is limited to VCC. The transfer characteristic with input and output waveforms is shown in Thus, this circuit behaves as a two-level clipper (slicer). The region of linearity can be controlled by the choice of VBB. FIGURE 4.20(a) A two-level transistor clipper