Commongateamplifier analogcmosdesign electronics tutorial. Voltage gain, output resistance, and input resistance of the mosfet common source amplifier, as well as why the common source amplifier is useful its everywhere. By analizing the small signal equivalent circuit, the. Cd stage amplifier is suitable for output stage of opamp due to its low output impedance and large bandwidth. Common gate lna cont substitute i2 s 4ktbgs and i2 d 4kt. The commonsource cs amplifier for mosfet is the analogue of the common. To solve for the voltage gain, we need expressions for v in and v out in terms of circuit components. To obtain the expression for v in, write the kvl equation around the gatesource loop.
The common gate amplifier has the highest output impedance of the three fet amplifier. A current buffer takes the input current which may have a relatively small norton resistance and replicates the current at the output port, which has a high output resistance input signal is applied to the source output is taken from the drain to first order, current gain. The ac output is taken from the drain terminal, and an external load r l is capacitorcoupled to the drain, exactly as in the case of a commonsource circuit. Figure below shows the small signal equivalent circuit of the cg amplifier. However, in cmos analog ic, cs stage is more widely used for output stage opamp than cd stage. By inspection, the input resistance of the common drain amplifier is rin rg r 1 r 2. The dc and ac parameters are analyzed and a circuit based on the values used in. Ece 315 spring 2007 farhan rana cornell university.
Vbias, rd and wl of mosfet selected to bias transistor in saturation and obtain desired output bias point i. The object is to solve for the smallsignal voltage gain, input resistance, and output resistance. The common gate amplifier is used as a current buffer amplifier, it has the relatively small input resistance and also relatively large output resistance. Dc solution a replace the capacitors with open circuits. Ece 255, mosfet basic configurations purdue engineering. Department of eecs university of california, berkeley eecs 105fall 2003, lecture 17 prof. The analogous bipolar junction transistor circuit is the commonbase amplifier. This video covers the characteristics of jfet common gate amplifiers. Mos common source amp current source active load common gate amp common drain amp. Common gate circuit equivalent circuit voltage gain. The common gate amplifier provides a power gain for the signal amplifier. Smallsignal model for pmos and for rest of circuit.490 592 110 408 673 340 1036 120 853 256 1170 412 521 857 947 1097 650 1035 598 626 580 141 275 310 228 920 561 805 31 1253 1414 1344 120 1235 595 84 1318 206 1047 642 1137 1024 629 1012 16 1205 727 1028 1150