I am designing a CS Amplifier in CADENCE Virtuoso with 2 nmos and 2pmos.The lower nmos is used for amplification and the upper nmos for casoding.The upper 2 pmos are used for current source and cascoding to improve output resiatance . But how do I bias the upper 3 trasistors in an IC ? In current mirror i need to give a reference current source .How do we make a reference current source in an IC ?
Hello, you need precision voltage, precision resisitant and one Op-Amp, you must tied one side of resistant to the voltage and another side to one port of Op-Amp, then you must tied another port of Op-Amp to the precision voltage, the output port of Op-Amp also must drive a P-channel transistor, then you can get require current by change precision voltage refrence.
Best regards.
Hi O-P.,
Several years ago, I also questioned myself about the same like you now. So I can summary the answer below:
(*) In the IC design using MOSFET, when bias the MOS device (NMOS and PMOS), we usually use the current mirror. And the question here is: in the current mirror, we need the "ideal current source". So how can we have this "ideal current source"? In fact, we have 2 basic techniques generate this "ideal current source" . Before entering the explain in detail, you should remember about the characteristic of a "ideal current source" (also named as: "reference current"): that is the independence of the output current with both of TEMPERATURE and SUPPLY VOLTAGE.
1. With the variation of supply voltage, we have a very well-known technique: SELF-BIAS current source (please see the book of Razavi: Analog CMOS Integrated Circuit - Chapter 5). This technique can be used to bias the other MOS devices basing on the fundamentals of current mirror. Remember that this technique generate a voltage reference (current reference) with a nice characteristic (quite insensitive with the supply variation), but owns a large dependence as temperature changes. However, if we use this technique in several applications such as design the OPAMPs, ... it is still OK.
2. The second technique is Bandgap Reference, this techniques generate a voltage reference whose characteristics are very good with supply voltage variation and temperature variation. However, the circuit is a little more complex as compare to the SELF-BIAS technique that I mentioned above. The bandgap reference circuit usually be used in the critical applications which requires a high quality of reference circuit such as: Converters, LDO,...
I hope my answer makes you understand a bit about the bias techniques.
BRs,
Nguyen Ha
If I were you, I would use an ideal current source to mirror the current to both nMOS and pMOS branches. For measurements, you can use a precision DC current from a power supply.
Yes, first you can use an ideal current source, as shown in Fig. 6 in https://www.researchgate.net/publication/256004523_Richardson_extrapolation-based_sensitivity_analysis_in_the_multi-objective_optimization_of_analog_circuits?ev=prf_pub
after you set the sizes of your circuit elements, then you can implement the ideal current source by the options listed by Van Ha Nguyen,
Article Richardson extrapolation-based sensitivity analysis in the m...
You can find a number of current references in the litterature which are designed to provide reference currents in ICs which can be mirrored for biasing purposes. I worked on a temperature-independent current reference several years ago.
I hope that the paper and its references could be useful.
Article A new compact temperature-compensated CMOS current reference
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