THS4521 Datasheet, PDF (24/65 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
8 Detailed Description
www.ti.com
8.1 Overview
The THS4521, THS4522, and THS4524 family is tested with the test circuits shown in this section; all circuits are
built using the available THS4521 evaluation module (EVM). For simplicity, power-supply decoupling is not
shown; see the layout in the Typical Applications section for recommendations. Depending on the test conditions,
component values change in accordance with Table 4 and Table 5, or as otherwise noted. In some cases the
signal generators used are ac-coupled and in others they dc-coupled 50-Ω sources. To balance the amplifier
when ac-coupled, a 0.22-μF capacitor and 49.9-Ω resistor to ground are inserted across R_IT on the alternate
input; when dc-coupled, only the 49.9-Ω resistor to ground is added across R_IT. A split power supply is used to
ease the interface to common test equipment, but the amplifier can be operated in a single-supply configuration
as described in the Typical Applications section with no impact on performance. Also, for most of the tests,
except as noted, the devices are tested with single-ended inputs and a transformer on the output to convert the
differential output to single-ended because common lab test equipment has single-ended inputs and outputs.
Similar or better performance can be expected with differential inputs and outputs.
As a result of the voltage divider on the output formed by the load component values, the amplifier output is
attenuated. The Atten column in Table 5 shows the attenuation expected from the resistor divider. When using a
transformer at the output (as shown in Figure 55), the signal sees slightly more loss because of transformer and
line loss; these numbers are approximate.
Table 4. Gain Component Values for Single-Ended Input (see Figure 54)
Gain
1 V/V
2 V/V
5 V/V
10 V/V
R_F
1 kΩ
1 kΩ
1 kΩ
1 kΩ
R_G
1 kΩ
487 Ω
191 Ω
86.6 Ω
R_IT
52.3 Ω
53.6 Ω
59.0 Ω
69.8 Ω
1. Gain setting includes 50-Ω source impedance. Components are chosen to achieve gain and 50-Ω input
termination.
Table 5. Load Component Values For 1:1 Differential To Single-Ended Output Transformer (See
Figure 55)
R_L
100 Ω
200 Ω
499 Ω
1 kΩ
R_O
24.9 Ω
86.6 Ω
237 Ω
487 Ω
R_OT
Open
69.8 Ω
56.2 Ω
52.3 Ω
Atten
6 dB
16.8 dB
25.5 dB
31.8 dB
1. Total load includes 50-Ω termination by the test equipment. Components are chosen to achieve load and 50-
Ω line termination through a 1:1 transformer.
24
Submit Documentation Feedback
Copyright © 2008–2015, Texas Instruments Incorporated
Product Folder Links: THS4521 THS4522 THS4524