Mumbai University > Computer Engineering > Sem 3 > Electronic Circuits and Communication Fundamentals

Marks: 5 Marks

Year: Dec 2013

The three biasing schemes are:

• Constant-voltage bias, which is most useful for RF and video amplifiers employing small dc drain resistors. Also known as voltage divider bias.
• Constant-current bias, which is best suited to low-drift dc amplifier applications such as source followers and source-coupled differential pairs. Also known as fixed bias.
• Self-bias (also called source bias or automatic bias), which is a somewhat universal scheme particularly valuable for ac amplifiers.

The Q-point established by the intersection of the load line and the VGS = –0.4 V output characteristic of Figure 1 provides a convenient starting point for the circuit comparison. The load line shows that a drain supply voltage, VDD, of 30 V and a drain resistance, RD, of 39 k are being used. The voltage divider biasing circuit provides better stability.