Simon Bjurek
--- a/b_asic/sfg_generators.py
+++ b/b_asic/sfg_generators.py
    output <<= tmp_add

    return SFG([input_op], [output], name=Name(name))
+
+
+def direct_form_1_iir(
+    b: Sequence[complex],
+    a: Sequence[complex],
+    name: Optional[str] = None,
+    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")