THS4521 Datasheet, PDF (30/65 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT, RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

THS4521, THS4522, THS4524
SBOS458H – DECEMBER 2008 – REVISED JUNE 2015
www.ti.com
8.3.8 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 62 shows the small-signal frequency
response with 1-kΩ and 10-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 kΩ and 10 kΩ
6
3
1 kΩ
0
–3
10 kΩ
–6
–9
–12
–15
–18 V_S+ = 5.0 V
–21 ^VO ^{= 100 mV}PP
–24 ^{Gain = 1 V/V}
0.1
1
10
100
Frequency (MHz)
1000
Figure 62. THS4521 Frequency Response With Various Gain Setting and Load Resistor Values
8.3.9 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 63 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
THS4522,
3
THS4524
0
THS4521
-3
THS4521
SOIC
MSOP
-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
10
100
1000
Frequency (MHz)
Figure 63. Small-Signal Frequency Response: Package Variations
30
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