Phase margin is an important specification for closed loop systems and in op amps specifically. It can be difficult to understand intuitively. A recent post by Signal Processing Group provides a way to understand this specification. Please visit our website and select the “complementary” tab and then access the article on phase margin.

# Author Archives: Ain

# Calculate the gain of a MOSFET in saturation in the strong inversion region given the drain current and the effective gate voltage

The product of the MOSFET transconductance ( KP/KN) and the aspect ratio ( W/L) is being labeled as the gain of the operating MOSFET. A simple calculator to do this is now available for a first order estimate on the Signal Processing Group website. Please check the “complementary” item menu in the SPG website for this and other items of interest.

# Calculate the current in the saturation region of a MOSFET in strong inversion

In analog CMOS design the MOSFET is usually operated in saturation where the IDS – VDS curves are close to being flat. The slight slope leads to the definition of the channel length modulation parameter. A simple calculator has been released by Signal Processing Group to allow a first order calculation of this current as starting points of a design. Please visit the SPG website and look under the “calculators” menu item.

# Calculate the body effect parameter for a MOSFET in strong inversion

The body effect parameter comes into play for analog CMOS design when the source and substrate is not connected to the same node but have a reverse bias voltage across them. It affects the threshold voltage of the MOSFET and thereby is critical to the operation of the MOSFET. Signal Processing Group has released a simple calculator to evaluate this parameter given the substrate doping and the gate capacitance. The solution is based on a first order model and is primarily useful as a starting point for design. Please visit the Signal Processing Group website for this and other very useful information.

# Calculate the surface potential of a MOSFET in strong inversion

The surface potential in a strongly inverted MOSFET is one of the component parameters in the calculation of current in strong inversion ( or for that matter in weak inversion) of a MOSFET. It is used in the calculation of the threshold voltage. It depends strongly on the surface concentration of the MOSFET and the intrinsic concentration of the substrate ( ni). Signal Processing Group has released a simple calculator for first order calculations of this important quantity. Please visit the Signal Processing Group website and look under the ” calculators” menu item to find this calculator as well as many others.

# Calculate the gm of a MOSFET in saturation

The gm of a MOSFET in saturation ( in the strong inversion region) is an important parameter for analog CMOS design. The hand calculation value is easy to calculate using a simple calculator such as the one that Signal Processing Group has released on their website. Please visit the Signal Processing Group website and look under the “calculators” menu.

# Calculate the effective gate voltage of a MOSFET in strong inversion

The effective gate voltage of a MOSFET in strong inversion is a critical design parameter for MOSFET analog and digital design. It provides the designer with a simple way to do hand calculations of the current and size of the device. A simple calculator has been released by Signal Processing Group that may be used to do this calculation as a starting point for more fine tuning by an advanced circuit simulator. Please visit our website and search under the “calculators” menu.

# Calculate the threshold voltage of a MOSFET in strong inversion with the body effect

The threshold voltage of a MOSFET in strong inversion is called the extrapolated threshold, VT0. This voltage is extracted by connecting the source to the substrate thus avoiding the effect of the reverse biased source – substrate junction ( VBS ). In order to calculate the threshold with body effect an equation is used ( hand calculations). This formulation includes constants such as VT0, GAMMA ( body effect parameter) and the surface potential in strong inversion ( 2phiF). A calculator to do this, written in javascript, has been released by Signal Processing Group Inc. and is available on the SPG website. Please visit for this, as well as other information.

# Calculate the transconductance of a MOSFET in strong inversion

The transconductance of a MOSFET is an important design parameter for CMOS design. This parameter and the threshold voltage form a pair of parameters that almost all CMOS design is based on. Signal Processing Group Inc. released a javascript calculator to calculate this parameter for quick CMOS design that can be trimmed to a final design using some nth order simulator. Hand calculations lay the foundation for design and providing a starting point for the designer. Please visit the SPG website for more options and information.

# COX calculator for MOSFETS.

COX is a critical design parameter for CMOS design. It is the capacitance generated by the gate oxide capacitance and is a parameter that generates the transconductance gain number for the MOSFET. A calculator for this parameter was posted by the team at Signal Processing Group Inc. to facilitate the designer’s task of designing CMOS circuits. It can be found under the “calculators” menu item on the SPG website.