Switched-Capacitor Circuits ( h t 10 4 10 5 10 6 t t f h t 11 D t t ...

High-Q Biquad Filter
• General transfer function:
V
Hz () o () z K 3 z 2 + K 1 K 5 + K 2 K 5 – 2K 3 z +K 3 – K 2 K 5
------------ = –-----------------------------------------------------------------------------------------------------------------
V i () z z 2 + K 4 K 5 + K 5 K 6 – 2z+1–
K 5 K 6
• The function can be rewritten as:
• The coefficients are then:
Hz ()
=
a 2 z 2 + a 1 z + a 0
–------------------------------------
z 2 + b 1 z+
b 0
K 1 K 5 = a 0 + a 1 + a 2
K 2 K 5 = a 2 – a 0
K 3 = a 2
K 4 K 5 =
1 + b 0 +
b 1
K 5 K 6 = 1–
b 0
• A signal-flow-graph approach is used to find the transfer function. There is some
freedom in chossing the coefficients as there is one less equation than the
number of coefficients. K4 = K5 = SQR (1+b0 + b1) defines the other ratios.