Where To Find This Example
Select Help > Open Examples... from the menus and type either the example name listed above or one of the keywords below.
Or in Version 13 or higher you can open the project directly from this page using this button.
HTML |
---|
<script src="https://s3.amazonaws.com/downloads.awrcorp.com/gh/ghcommon.bas" type="text/awrscript"> </script> <button class="gh-button gh-projectopen" onclick="runAwrScript('awrGhOpenProject','Band_Gap_with_PVT.emp')">Open Install Example</button> |
Design Notes
Band Gap with Process/Voltage/Temperature (PVT) Variations and Noise Contributors
Overview
To demonstrate the ease by which noise and PVT variation can be simulated, a band gap bias network with a simple topology is used in this project. The primary purpose of the band gap circuit is a temperature stable output voltage. In addition, noise is equally important. In this example, we show both of these analyses along with noise contributors from individual circuit elements.
Band Gap Testbench Setup
The Band Gap test bench is the top level schematic. Upon descending down to the lower level sub circuit called band_gap_generator, we see the simple cross-quad of BJT's to generate the PTAT (Proportional To Absolute Temperature) current. After running the simulation (choose Simulate > Analyze) the PTAT current from the cross-quad is plotted in the Graph titled Iout vs. PVT.
The cross-quad PTAT current is mirrored into the branch of transistors on the right where a PTAT voltage is formed across the lower resistor, R4.
This voltage is then added to Vbe to form a band gap voltage. The value of R4 is optimized for the correct temperature response shown in the Graph titled VBG vs. PVT.
The variable _TEMP is a system variable which can be swept like any other variable. We use it here in the SWPVAR block. The response has been manually tuned for flat response from 0 to 100 deg C. VCC is the next variable used in a SWPVAR block and finally process corners [Nominal, Fast, and Slow] are used in the last SWPVAR block. Notice the variable "corners" is set to numerical values [0, 1, 2] corresponding to [Nominal, Fast, Slow].
Other Measurements
The next Graph titled Band Gap Noise vs. Freq and PVT simply measures the output noise of our circuit.
Currently, there is one small trick to simulate the AC noise of a circuit without an AC source. We have made the VCC supply originate from the ACVS instead of the DCVS. We set the AC mag = 0 and set the DC value to the desired supply voltage. In this way, we can specify the frequency sweep in the Project Options as the noise frequencies to simulate. The V_NSMTR is placed at the output node where we want to measure noise. If we were measuring Noise Figure of a 2-port network, we would need to specify a voltage or current source as the input reference. Here, we specify our supply voltage source, but it does not affect the measurement since we are only interested in total output noise. However, we still specify a source for V_NSMTR to function properly.
Finally, the noise contributors are listed in a Graph titled Noise Contributors. The list contains all the elements of the circuit with their individual contribution to the total output noise.