Datasheet

TPA6204A1
SLOS429B − MAY 2004 − REVISED SEPTEMBER 2009
www.ti.com
8
APPLICATION INFORMATION
FULLY DIFFERENTIAL AMPLIFIER
The TPA6204A1 is a fully differential amplifier with
differential inputs and outputs. The fully differential
amplifier consists of a differential amplifier and a common-
mode amplifier. The differential amplifier ensures that the
amplifier outputs a differential voltage that is equal to the
differential input times the gain. The common-mode
feedback ensures that the common-mode voltage at the
output is biased around V
DD
/2 regardless of the common-
mode voltage at the input.
Advantages of Fully Differential Amplifiers
D Input coupling capacitors not required: A fully
differential amplifier with good CMRR, like the
TPA6204A1, allows the inputs to be biased at voltage
other than mid-supply. For example, if a DAC has
mid-supply lower than the mid-supply of the
TPA6204A1, the common-mode feedback circuit
adjusts for that, and the TPA6204A1 outputs are still
biased at mid-supply of the TPA6204A1. The inputs of
the TPA6204A1 can be biased from 0.5 V to V
DD
−
0.8 V. If the inputs are biased outside of that range,
input coupling capacitors are required.
D Mid-supply bypass capacitor, C
(BYPASS)
, not
required: The fully differential amplifier does not
require a bypass capacitor. This is because any shift
in the mid- supply affects both positive and negative
channels equally and cancels at the differential
output. However, removing the bypass capacitor
slightly worsens power supply rejection ratio (k
SVR
),
but a slight decrease of k
SVR
may be acceptable when
an additional component can be eliminated.
D Better RF-immunity: GSM handsets save power by
turning on and shutting off the RF transmitter at a rate
of 217 Hz. The transmitted signal is picked-up on input
and output traces. The fully differential amplifier
cancels the signal much better than the typical audio
amplifier.
APPLICATION SCHEMATICS
Figure 15 through Figure 17 show application schematics
for differential and single-ended inputs. Typical values are
shown in Table 1.
Table 1. Typical Component Values
COMPONENT VALUE
R
I
40 kΩ
C
(BYPASS)
(1)
0.22 µF
C
S
1 µF
C
I
0.22 µF
(1)
C
(BYPASS)
is optional
_
+
V
DD
V
O+
V
O−
GND
6
5
8
7
To Battery
C
s
Bias
Circuitry
IN−
IN+
4
3
2
+
−
In From
DAC
SHUTDOWN
R
I
R
I
1
C
(BYPASS)
(1)
100 kΩ
40 kΩ
40 kΩ
(1)
C
(BYPASS)
is optional
Figure 15. Typical Differential Input Application Schematic