Re: OTA design step by step
these are some general steps for start:
1- if you have a limit for your power consumption, you can calculate your total allowalbe current (by knowing the value of your power supply)... if not,assume a reasonable limit, maybe around 5-10mw for 1.8v power supply
2- By writting the equations of Gain, settling time, unity-gain bandwidth and the poles of your system, you can find some limits for your currents and Gm.
3- for finding a transistor's W/L you need at least 2 of these parameters : I, Gm and Veff. so if you couldnt find 2of these from previous steps, you should start assuming some values....one of the values that can help is the Veff, which also effects your Maximum Swing and a typical value for a 1.8 power supply can be 200mv... by finding 2of these you can start calculating W/L.
4- by writting the equations you can find the relation between differet parameters, but for some help L has a considerable effect on Rds, you can increase it for more gain, but rememeber high W & L will increase the capacitances and the speed of your circuit.
5- for some constants like µC(oxide) and λ, simulation of a single transistor in your desired technology (like 0.18u or 0.13u) can help a lot, for 0.18u i usually consider an initial guess of µ
C(ox) = 200µ and µ(p)C(ox) = 50µ
hope it can help you for start
message me if you need more.....