THS6184_16 Datasheet, PDF (21/39 Pages) Texas Instruments – DUAL-PORT, LOW-POWER DIFFERENTIAL xDSL LINE DRIVER AMPLIFIERS

THS6184
www.ti.com ................................................................................................................................................. SLLS635D – AUGUST 2005 – REVISED JANUARY 2009
OFFSET VOLTAGE
The output offset voltage, (V_OO) is the sum of the input offset voltage (V_IO) and both input bias currents (I_IB) times
the corresponding gains. The following schematic and formula can be used to calculate the output offset voltage:
R_F
R_G
 _IIB−
−
+
V_O
R_S
−
+
 _IIB+
V_IO
ǒ Ǔ ǒ Ǔ VOO + VIO
1
)
RF
RG
" IIB₎ RS
1
)
RF
RG
" IIB_* RF
Figure 53. Output Offset Voltage Model
NOISE CALCULATIONS
Noise can cause errors on very small signals. This is especially true for the amplifying small signals. The noise
model for current feedback amplifiers (CFB) is the same as voltage feedback amplifiers (VFB). The only
difference between the two is that the CFB amplifiers generally specify different current noise parameters for
each input while VFB amplifiers usually only specify one noise current parameter. The noise model is shown in
Figure 54. This model includes all of the noise sources as follows:
• e_n = Amplifier internal voltage noise (nV/√Hz)
• IN+ = Noninverting current noise (pA/√Hz)
• IN- = Inverting current noise (pA/√Hz)
• e_RX = Thermal voltage noise associated with each resistor (e_RX = √4 kTR_x)
R_S
e_Rs
e_n
Noiseless
e_ni
+
_
e_no
IN+
e_Rf
R_F
IN−
e_Rg
R_G
Figure 54. Noise Model
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