Datasheet

IN-
OUT-
IN+
OUT+
200 W
+5V
1k W
B0toB5
0.1 Fm
75 W
From50-
Source
W
V
MID2
0.1 Fm
V
MID1
0.1 Fm
LM
(1)
GS
(1)
PD
PGA870
0.1 Fm
B0toB5
PGA870
SBOS436A –DECEMBER 2009–REVISED FEBRUARY 2011 www.ti.com
Single-Ended to Differential Operation
Figure 45 represents a single-ended to differential conversion test configuration with a 50-Ω source and a 200-Ω
load. The midsupply pins V
MID1
and V
MID2
are properly bypassed; because this circuit is ac-coupled, these pins
provide the biasing voltage required by the PGA870 input stage. The LATCH MODE, GAIN STROBE, and PD
pins are connected to the supply voltage through a pull-up resistor. The PD pin set high powers up the PGA870,
while setting the LATCH MODE and GAIN STROBE pins high bypasses the latch mode, allowing instantaneous
gain changes as B5 to B0 change. On the noninverting input, a 75-Ω resistance was added to adapt the 150 Ω to
50 Ω and match the 50-Ω source.
If a single-ended signal source is to be dc-coupled to the device, its voltage swing should be centered about the
midsupply reference, V
MID1
. If the input dc voltage is greater than 0.2 V from midsupply, then increased distortion
and reduced performance can result. The non-driven input pin of the PGA870 should be ac-coupled to ground
through a capacitor. In this configuration, the PGA870 amplifies the difference between the dc-coupled input
signal and the midsupply reference.
(1) LM = LATCH MODE pin (pin 1), GS = GAIN STROBE pin (pin 7).
Figure 45. Basic Connections for Single-Ended to Differential Conversion
18 © 2009–2011, Texas Instruments Incorporated
Product Folder Link(s): PGA870