THS4521 Datasheet, PDF (27/43 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT, RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

THS4521
THS4522
THS4524
www.ti.com.................................................................................................................................................... SBOS458B – DECEMBER 2008 – REVISED MAY 2009
Low-Power Applications and the Effects of
Resistor Values on Bandwidth
For low-power operation, it may be necessary to
increase the gain setting resistors values to limit
current consumption and not load the source. Using
larger value resistors lowers the bandwidth of the
THS4521, THS4522, and THS4524 family as a result
of the interactions between the resistors, the device
parasitic capacitance, and printed circuit board (PCB)
parasitic capacitance. Figure 64 shows the
small-signal frequency response with 1-kΩ, 10-kΩ,
and 100-kΩ resistors for R_F, R_G, and R_L (impedance
is assumed to typically increase for all three resistors
in low-power applications).
SMALL-SIGNAL FREQUENCY RESPONSE
Gain = 1, R_F = R_G = R_L = 1 kW, 10 kW, 100 kW
6
3
1 kW
0
-3
10 kW
-6
-9
100 kW
-12
-15
-18 V_S+ = 5.0 V
-21 ^VO ^{= 100 mV}PP
Gain = 1 V/V
-24
0.1
1
10
100
Frequency (MHz)
1000
Frequency Response Variation due to
Package Options
Users can see variations in the small-signal (V_OUT =
100 mV_PP) frequency response between the available
package options for the THS4521, THS4522, and
THS4524 family as a result of parasitic elements
associated with each package and board layout
changes. Figure 65 shows the variance measured in
the lab; this variance is to be expected even when
using a good layout.
SMALL-SIGNAL FREQUENCY RESPONSE
Device and Package Option Comparison
6
3
0
-3
-6
-9
-12
-15 _{VS+ = 5.0 V}
-18 ^{Gain = 1 V/V}
-21
R_F = 1 kW
R_L = 1 kW
-24
0.1
1
THS4521
MSOP
THS4522,
THS4524
THS4521
SOIC
10
100
Frequency (MHz)
1000
Figure 65. Small-Signal Frequency Response:
Package Variations
Figure 64. THS4521 Frequency Response with
Various Gain Setting and Load Resistor Values
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Product Folder Link(s): THS4521 THS4522 THS4524