Datasheet

APPLICATION INFORMATION
FULLY DIFFERENTIAL AMPLIFIER
APPLICATION SCHEMATICS
Advantages of Fully Differential Amplifiers
_
+
V
DD
V
O+
V
O-
GND
ToBattery
C
s
Bias
Circuitry
IN-
IN+
+
-
InFrom
DAC
SHUTDOWN
R
I
R
I
C
( )
BYPASS
(Optional)
R
F
R
F
TPA6203A1
www.ti.com .......................................................................................................................................................... SLOS364F – MARCH 2002 – REVISED JUNE 2008
negative channels equally and cancels at the
differential output. However, removing the bypass
capacitor slightly worsens power supply rejection
The TPA6203A1 is a fully differential amplifier with
ratio (k
SVR
), but a slight decrease of k
SVR
may be
differential inputs and outputs. The fully differential
acceptable when an additional component can be
amplifier consists of a differential amplifier and a
eliminated (see Figure 17 ).
common- mode amplifier. The differential amplifier
• Better RF-immunity: GSM handsets save power
ensures that the amplifier outputs a differential
by turning on and shutting off the RF transmitter at
voltage that is equal to the differential input times the
a rate of 217 Hz. The transmitted signal is
gain. The common-mode feedback ensures that the
picked-up on input and output traces. The fully
common-mode voltage at the output is biased around
differential amplifier cancels the signal much
V
DD
/2 regardless of the common- mode voltage at the
better than the typical audio amplifier.
input.
• Input coupling capacitors not required: A fully Figure 28 through Figure 30 show application
differential amplifier with good CMRR, like the schematics for differential and single-ended inputs.
TPA6203A1, allows the inputs to be biased at Typical values are shown in Table 1 .
voltage other than mid-supply. For example, if a
DAC has mid-supply lower than the mid-supply of Table 1. Typical Component Values
the TPA6203A1, the common-mode feedback
COMPONENT VALUE
circuit adjusts for that, and the TPA6203A1
R
I
10 k Ω
outputs are still biased at mid-supply of the
R
F
10 k Ω
TPA6203A1. The inputs of the TPA6203A1 can
be biased from 0.5 V to V
DD
- 0.8 V. If the inputs
C
(BYPASS)
(1)
0.22 µ F
are biased outside of that range, input coupling
C
S
1 µ F
capacitors are required.
C
I
0.22 µ F
• Mid-supply bypass capacitor, C
(BYPASS)
, not
(1) C
(BYPASS)
is optional
required: The fully differential amplifier does not
require a bypass capacitor. This is because any
shift in the mid-supply affects both positive and
Figure 28. Typical Differential Input Application Schematic
Copyright © 2002 – 2008, Texas Instruments Incorporated Submit Documentation Feedback 9
Product Folder Link(s): TPA6203A1