diff --git a/content/zettels/analog_to_digital_converters.md b/content/zettels/analog_to_digital_converters.md
index b2f1f3a..36c203c 100644
--- a/content/zettels/analog_to_digital_converters.md
+++ b/content/zettels/analog_to_digital_converters.md
@@ -8,6 +8,11 @@ Tags
 : [Electronics]({{< relref "electronics" >}})
 
 
+## Types of Analog to Digital Converters {#types-of-analog-to-digital-converters}
+
+-   Delta Sigma ([Baker 2011](#org1a9e622))
+
+
 ## Power Spectral Density of the Quantization Noise {#power-spectral-density-of-the-quantization-noise}
 
 This analysis is taken from [here](https://www.allaboutcircuits.com/technical-articles/quantization-nois-amplitude-quantization-error-analog-to-digital-converters/).
@@ -23,9 +28,9 @@ Let's suppose that the ADC is ideal and the only noise comes from the quantizati
 Interestingly, the noise amplitude is uniformly distributed.
 
 The quantization noise can take a value between \\(\pm q/2\\), and the probability density function is constant in this range (i.e., it’s a uniform distribution).
-Since the integral of the probability density function is equal to one, its value will be \\(1/q\\) for \\(-q/2 < e < q/2\\) (Fig. [1](#org2f8924a)).
+Since the integral of the probability density function is equal to one, its value will be \\(1/q\\) for \\(-q/2 < e < q/2\\) (Fig. [1](#orga9627b6)).
 
-<a id="org2f8924a"></a>
+<a id="orga9627b6"></a>
 
 {{< figure src="/ox-hugo/probability_density_function_adc.png" caption="Figure 1: Probability density function \\(p(e)\\) of the ADC error \\(e\\)" >}}
 
@@ -76,4 +81,7 @@ The quantization is:
 
 {{< youtube b9lxtOJj3yU >}}
 
-<./biblio/references.bib>
+
+## Bibliography {#bibliography}
+
+<a id="org1a9e622"></a>Baker, Bonnie. 2011. “How Delta-Sigma Adcs Work, Part.” _Analog Applications_ 7.