Saturday, December 16

Phase splitter

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To make a phase splitter circuit we can use a transistor phase splitter circuit.The input is at the base of transistor, and the outputs are at the collector and emitter terminals. The voltage divider circuit provides a stable base voltage that is high enough to forwaed bias tranasistor for all ac in put signal conditions.Because transistor is always forward biased for 360 degrees of the input signal, there is no amplitude distortion of the output signals.In a tranasistor phase splitter circuit, the emiter resistor and collector resistor are equal.So the voltage drop across the collector circuit equal to the emitter circuit voltage drop and the voltage gain at the collector equals the voltage gain ar the emitter.To summarize, a transistor phase splitter is a common emitter circuit that converts the input signal into two output signals that ate 180 degrees out of phase with peak to peak voltages essentially equal to the input signal.

Phase splitter DC operation:

The transistor phase splitter circuit has a single npn transistor which is connected common emitter circuit.The ac input is capacitor coupled  to the transistor base.Output collector is capacitor coupled to the collector terminal.Output emitter is capacitor coupled to the emitter terminal.The ac input and outputs capacitor coupled to isolate the transistor dc voltages from the ac input and outputs.The base voltage forward biases the base emitter junction for all ac input signals.In transistor circuits, the emitter and collector currents are essentially equal because the base current is very small. The emitter current is the sum of the collector and base currents.In a transistor phase splitter circuit, the collector resistor and the emitter resistor have the same value. The teansistor phase splitter is unlike many other transistor configurations because the dc voltage drops in the emiiter and collector cricuits are equal.As a result, the peak to peak voltages of the ac waveform at output collector and emitter are equal.Because the transistor phase splitter is biased for class A operation, the ac input signal does not affect I total because Vb is high. A short between the base and emitter turns off the transistor.

Voltage gain and phase relationships: With the ac signal is input to the base of the phase splitter circuit, the ac signal( voltage) at ouput emitter is in phase with the input signal and the ac signal( voltage) at output collector is 180 out of phase with the input signal. Although the ac voltages at the emitter and collector are 180 degrees out of phase but thee ax currents at the input, emitter, and collector in phase. The ac current at the emitter increases as the current at the input increases, the ac emitter current is in phase with the input current.Because the emitter and collector currents are essentially equal, the collector current is in phase with the emitter current. When calculating voltage gains from measured input and output voltage, you do not need to convert voltages from peak to peak to rms values. Only the ratio of output to input voltages is important, the units cancel. The resistance of the emitter terminal is denoted by re’.The approximate value of re’ is expressed below

Re’=26mV/Ie.

The resitive value is small compared to R emitter. Because the emitter current cancels out, gain at output emitter can also be calculated from the equation:

Av= Remitter/(Remitter+re’). Because re’ is small compared to Remitter so Av is slightly less than 1.0. Assume that the collector and emitter currents are equal, and neglect the small value of re’. The gain at output collector then equals the collector resistor divided by the emitter resistor. Av emitter and Av collector are both 1, therefore the amplitude relationship of output signal emitter and collector equal amplitude.

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