THS4141CDGNR Datasheet, PDF (14/33 Pages) Texas Instruments – HIGH-SPEED FULLY DIFFERENTIAL I/O AMPLIFIERS

THS4140
THS4141
SLOS320F – MAY 2000 – REVISED JANUARY 2006
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APPLICATION INFORMATION (continued)
The transfer function for this filter circuit is:
ȧȧȡȢ _{ǒ Ǔ} ȧȧȣȤ _{ȧȡȢ ȧȣȤ Hd(f) +}
K
x
–
f
FSF x fc
2
)
1
Q
jf
FSF x fc
)
1
Rt
2R4 ) Rt
1
)
j2πfR4RtC3
2R4 ) Rt
Where K +
R2
R1
(2)
FSF x fc
+
1
2π ^Ǹ2 x R2R3C1C2
and
Q
+
R3C1
Ǹ_{2 x R2R3C1C2}
) R2C1 ) KR3C1
(3)
K sets the pass band gain, fc is the cutoff frequency for the filter, FSF is a frequency-scaling factor, and Q is the
quality factor.
Ǹ ^Ǹ _{FSF +}
Re² ) |Im|² and Q +
Re² ) |Im|²
2Re
(4)
Where Re is the real part, and Im is the imaginary part of the complex pole pair. Setting R2 = R, R3 = mR,
C1 = C, and C2 = nC results in:
FSF x fc
+
2πRC
1
Ǹ₂
x
mn
and Q
+
1
Ǹ_{2 x mn}
) m(1 ) K)
(5)
Start by determining the ratios, m and n, required for the gain and Q of the filter type being designed, then select
C and calculate R for the desired fc.
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