Differences

This shows you the differences between two versions of the page.

@@ Line 1: / Line 1: @@
+====== Schematic geometry ======
+Verilog-AMS defines hierarchical parameters ''$xposition'' and ''$yposition'' as well as ''$angle'' to express physical location and orientation as on a wafer or PCB. According to the LRM, ''$angle'' is supposed to mean "counter-clockwise".
+Our interpretation of counter-clockwise follows when choosing the x axis pointing to the right, and the y axis pointing upwards. Now a 90 degree rotation moves the x axis to the y axis, in other words ''(x,y)=(1,0)'' to ''(0,1)''. Equivalently, the y axis may be thought of as the imaginary axis in the complex plane. Then, rotation by 2\pi\phi corresponds to multiplication by exp(2\pi\phi * i), with the imaginary unit i.
+This seems relevant when moving on to schematics. Since Verilog-AMS is governed by physical semantics, we retain this choice of angle and coordinates also for schematic drawings, even though other coordinate systems are in common use.
+If you prefer a y axis pointing downwards, you may use a flipped coordinate system locally, as within the body of the following module.
+As expected, any uses of ''angle'' inside the body will be applied before the final vflip.
+<code>
+(* S0_vflip=-1 *)
+module upside_down_module();
+  [..]
+endmodule
+</code>
+====== Schematic Units ======
+The distance unit in a schematic is 1 meter. Some schematic editors use pixels on a screen or similar concepts. We use a scaling attribute to allow tools to interpret coordinates in their own way.
+<code>
+(* S0_scale=1000000 *)
+module many_pixel_module();
+  [..] // 1000000 is 1 meter.
+endmodule
+</code>