diff --git a/content/zettels/transconductance_amplifiers.md b/content/zettels/transconductance_amplifiers.md
index 54a5670..5be1d01 100644
--- a/content/zettels/transconductance_amplifiers.md
+++ b/content/zettels/transconductance_amplifiers.md
@@ -208,7 +208,26 @@ W_stop = 0.0025 [W]
 
 ## Basic Circuits {#basic-circuits}
 
-{{< figure src="/ox-hugo/okyay16_current_amplifier_schematic.png" caption="<span class=\"figure-number\">Figure 1: </span>From <&okyay16_mechat_desig_dynam_contr_metrol>, Appendix A" >}}
+
+### Howland Current Sources {#howland-current-sources}
+
+See Section 4.2.5 in <&horowitz15_art_of_elect_third_edition>.
+
+Howland current source is shown in Figure <fig:art_electronics_current_source>.
+
+> The output current is sourced through a sense resistor \\(R\_s\\) whose value you can choose independently of the matched resistor array (with resistor pairs \\(R\_1\\) and \\(R\_2\\)).
+> The best way to understand this circuit is to think of \\(IC\_1\\) as a difference amplifier whose output sense and reference connections sample the drop across \\(R\_s\\) (i.e., the current); the latter is buffered by follower IC2 so there is no current error.
+
+<a id="figure--fig:art-electronics-current-source"></a>
+
+{{< figure src="/ox-hugo/art_electronics_current_source.png" caption="<span class=\"figure-number\">Figure 1: </span>From <&horowitz15_art_of_elect_third_edition>" >}}
+
+
+### Other circuits found in the litterature {#other-circuits-found-in-the-litterature}
+
+{{< figure src="/ox-hugo/lafarga24_current_amplifier.png" caption="<span class=\"figure-number\">Figure 2: </span>From <&lafarga24_activ_vibrat_isolat_system_space_applic>, Appendix B" >}}
+
+{{< figure src="/ox-hugo/okyay16_current_amplifier_schematic.png" caption="<span class=\"figure-number\">Figure 3: </span>From <&okyay16_mechat_desig_dynam_contr_metrol>, Appendix A" >}}
 
 
 ## Estimation of the required current noise {#estimation-of-the-required-current-noise}
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