THS4150CDGN Datasheet, PDF (16/34 Pages) Texas Instruments – HIGH-SPEED DIFFERENTIAL I/O AMPLIFIERS

THS4150
THS4151
SLOS321G – MAY 2000 – REVISED MARCH 2009........................................................................................................................................................... www.ti.com
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
FSF x fc
+
1
2π ^Ǹ2 x R2R3C1C2
and
Q
+
R3C1
Ǹ_{2 x R2R3C1C2}
) R2C1 ) KR3C1
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
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)
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.
PRINCIPLES OF OPERATION
THEORY OF OPERATION
The THS415x is a fully differential amplifier. Differential amplifiers are typically differential in/single out, whereas
fully differential amplifiers are differential in/differential out.
Differential Amplifier
R_f
R_(g)
_
+
R_(g)
R_f
THS415x
Fully differential Amplifier
V_CC+
V_IN-
_
+
V_O+
V_IN+
_
+
V_O-
V_OCM
V_CC-
Figure 36. Differential Amplifier Versus a Fully Differential Amplifier
To understand the THS415x fully differential amplifiers, the definition for the pinouts of the amplifier are provided.
16
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