4410-4412/RAM: add amplitude ramp example

4410-4412.tex

@@ -566,11 +566,59 @@ Urukul was operated with a 50$\Omega$ termination to produce the waveform.
 \end{axis}
 \end{tikzpicture}
 
-\begin{figure}[h]
-    \centering
-    \includegraphics[width=\textwidth]{ad9910_amp_mod.png}
-    \caption{Expected waveform from the RAM modulation example}
-\end{figure}
+\subsection{Simple Amplitude Ramp (AD9910 Only)}
+An amplitude ramp of an RF signal can be generated by modifying the \texttt{self.amp} array in the previous example.
+\begin{minted}{python}
+def prepare(self):
+    # Reversed Order
+    self.amp = [1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.0]
+    self.asf_ram = [0] * len(self.amp)
+\end{minted}
+
+The generated RF output has an incrementing amplitude scale factor (ASF), increasing by 0.1 at every microsecond.
+Once the ASF reaches 1.0, it drops back to 0.0 at the next microsecond.
+The expected waveform over 1 cycle is plotted on the following figure.
+Note that phase of the RF pulses may drift gradually.
+Urukul was operated with a 50$\Omega$ termination to produce the waveform.
+
+\begin{tikzpicture}[
+    declare function={
+        func(\x)= and(\x>=0, \x<1) * (0) +
+            and(\x>=1, \x<2) * (0.05*cos(deg(10*pi*\x))) +
+            and(\x>=2, \x<3) * (0.1*cos(deg(10*pi*\x))) +
+            and(\x>=3, \x<4) * (0.15*cos(deg(10*pi*\x))) +
+            and(\x>=4, \x<5) * (0.2*cos(deg(10*pi*\x))) +
+            and(\x>=5, \x<6) * (0.25*cos(deg(10*pi*\x))) +
+            and(\x>=6, \x<7) * (0.3*cos(deg(10*pi*\x))) +
+            and(\x>=7, \x<8) * (0.35*cos(deg(10*pi*\x))) +
+            and(\x>=8, \x<9) * (0.4*cos(deg(10*pi*\x))) +
+            and(\x>=9, \x<10) * (0.45*cos(deg(10*pi*\x))) +
+            and(\x>=10, \x<11) * (0.5*cos(deg(10*pi*\x)));
+    }
+]
+\begin{axis}[
+    axis x line=middle, axis y line=middle,
+    every axis x label/.style={
+        at={(ticklabel* cs:1.05)},
+        anchor=west,
+    },
+    every axis y label/.style={
+        at={(ticklabel* cs:1.05)},
+        anchor=south,
+    },
+    minor tick num=4,
+    grid=both,
+    height=8cm,
+    width=16cm,
+    ymin=-0.7, ymax=0.7, ytick={-0.5,...,0,...,0.5}, ylabel=Voltage ($V$),
+    xmin=0, xmax=11.5, xtick={0,...,11}, xlabel=Time ($\mu s$),
+]
+
+\addplot[blue, samples=1500, domain=0:11]{func(x)};
+\end{axis}
+\end{tikzpicture}
+
+\newpage
 
 Multiple RAM channels can also be synchronized.
 Similar to the 10 MHz single-tone RF signals, specify \texttt{phase} when calling \texttt{dds.set()} in \texttt{configure\char`_ram\char`_mode}.