Device Designer Overview

AnaSoft's Device DesignerTM is a first in Spice simulation. Traditionally, in legacy Spice simulation applications, users were forced to always use Spice as an analysis tool. That is, component values were chosen and then simulations were ran to see if the node voltages and device currents were at their desired values. The advanced Device DesignerTM feature of AnaSoft's SuperSpice removes this restriction for the design of a circuits DC operating conditions. Device DesignerTM allows device currents and voltages to be specified, and then have the values of resisters and mosfet sizes automatically determined and placed on the schematic.

Setting currents in a device, forces the devices value to be whatever it needs to be to ensure that that current flows.

Setting a device to be controlled by a pin/node voltage, forces that devices value to be whatever it needs to be to ensure that that voltage appears at that node.

Device Designer Operation

1 Double click on wires (or "q" them), and set their designer voltage.

2a Double click on resistors, and set their designer mode or designer current. Pin ID=0 is the positive node, Pin ID=1 is the negative node. The pin ID will be displayed in the windows status bar when the mouse is over the pin.

and/or

2b Double click on mosfets, and set their designer mode or designer current.

3 Run the simulator in design mode, which is the blue "D" button or the "\Run\DeviceDesigner" menu. The schematic will be automatically updated with the design results.

4 Set the device designer options as described below.

4 Run a normal simulation to verify the accuracy of the designed values.

Designer voltages are set via the circuit wire nodes. They are forced to these values by the specifications of the resisters and mosfet pins setup in their respective dialog setups.

Device Designer Options

The menu item "\Setups\Designer Setup" (or toolbar button "DD") brings up a dialog to set the run mode of the Designer. The options allow for selectively enabling the design of resisters ands mosfet values. Only selected values will be designed for, and updated on the schematic.

Example Design:

Load the DeviceDesigner.sss example into SuperSpice, and use the "\Run\DeviceDesigner" menu to run the designer.

Device Designer Help Notes

Do not over specify the circuit. Only the minimum required voltages and currents should be set. For example, if two series devices are set to force currents into each other, the Device Designer will almost certainly fail to find a solution.

To effectively use Device Designer, the basic operation of the circuit should be understood. Device Designer, will calculate the values based on specifications, however, it does not know if those specifications are compatible with each other. For example, setting the current in one pin of a transistor is usually sufficient. Do not use two devices to set a voltage on the same node.

Singular matrix - usually due to forcing currents from two series devices. Disable one of the devices designer attribute, or set it to a different one.

Setting designer voltages on nodes connecting to power supplies will fail. Make sure no device node setup is trying to do this.

Device Designer Cavorts

1 Width and Length designs are available for mosfet level 1 and 2.

2 Width designs only are available for BSim3v3 level (8/49) mosfets.

3 Due to the complicated formulas associated with the BSim3v3 model, there can be a small error in the determined value of the width.

4 The designer is not guaranteed to always find a solution. There are two accuracy options that can be set to help alleviate this issue. They are set in the "SS" Spice Options tab. These are "Designer Current Accuracy", "ssdesv" and "Designer Voltage Accuracy, "ssdesi". The current accuracy option is a direct setting of accuracy, that is, accuracy is 1/value. Its default is 10,000 which is 0.01%. The voltage accuracy value is a number that is associated with the accuracy and the final value of the calculated resistance. Larger resistances give more accurate values with the same setting of this option. Low resisters below 1 ohm, may require a larger value. Its default value is 100. This may be too high for very high resistance values.