diff --git a/b_asic/sfg_generators.py b/b_asic/sfg_generators.py
index 789cd1618e7ef6ae025eca6b99e53ba28214ca57..998c20a80ba1e8a8b9795afa3f1523d9309fd017 100644
--- a/b_asic/sfg_generators.py
+++ b/b_asic/sfg_generators.py
@@ -264,6 +264,7 @@ def direct_form_1_iir(
     mult_properties: Optional[Union[Dict[str, int], Dict[str, Dict[str, int]]]] = None,
     add_properties: Optional[Union[Dict[str, int], Dict[str, Dict[str, int]]]] = None,
 ) -> SFG:
+    """Generates a direct-form IIR filter of type I with coefficients a and b."""
     if len(a) != len(b):
         raise ValueError("size of coefficient lists a and b are not the same")
     if name is None:
@@ -318,6 +319,7 @@ def direct_form_2_iir(
     mult_properties: Optional[Union[Dict[str, int], Dict[str, Dict[str, int]]]] = None,
     add_properties: Optional[Union[Dict[str, int], Dict[str, Dict[str, int]]]] = None,
 ) -> SFG:
+    """Generates a direct-form IIR filter of type II with coefficients a and b."""
     if len(a) != len(b):
         raise ValueError("size of coefficient lists a and b are not the same")
     if name is None: