TA0103A Tripath Technology Inc., TA0103A Datasheet - Page 16

• Manufacturer Part Number: TA0103A
• Manufacturer: Tripath Technology Inc.

Performance Measurements of a TA0103A Amplifier
Tripath amplifiers operate by modulating the input signal with a high-frequency switching pattern.
This signal is sent through a low-pass filter (external to the Tripath amplifier) that demodulates it to
recover an amplified version of the audio input. The frequency of the switching pattern is spread
spectrum and typically varies between 200kHz and 1.5MHz, which is well above the 20Hz – 22kHz
audio band. The pattern itself does not alter or distort the audio input signal but it does introduce
some inaudible noise components.
The measurements of certain performance parameters, particularly those that have anything to do
with noise, like THD+N, are significantly affected by the design of the low-pass filter used on the
output of the TA0103A and also the bandwidth setting of the measurement instrument used. Unless
the filter has a very sharp roll-off just past the audio band or the bandwidth of the measurement
instrument ends there, some of the inaudible noise components introduced by the Tripath amplifier
switching pattern will get integrated into the measurement, degrading it.
One advantage of Tripath amplifiers is that they do not require large multi-pole filters to achieve
excellent performance in listening tests, usually a more critical factor than performance
measurements. Though using a multi-pole filter may remove high-frequency noise and improve
THD+N type measurements (when they are made with wide-bandwidth measuring equipment), these
same filters can increase distortion due to inductor non-linearity. Multi-pole filters require relatively
large inductors, and inductor non-linearity increases with inductor value.
Efficiency Of A TA0103A Amplifier
The efficiency, K, of an amplifier is:
The power dissipation of a TA0103A amplifier is primarily determined by the on resistance, R
the output transistors used, and the switching losses of these transistors, P
amplifier, P
For an 155W RMS per channel, 8: load amplifier using STW38NB20 MOSFETs, and an R
50m:,
In the above calculation the R
to account for some temperature rise of the MOSFETs. (R
as for a typical MOSFET as temperature increases from 25ºC to 170ºC.)
So,
This compares to the 90% measured efficiency (see Typical Performance graphs).
16
K = P
P
where:
P
P
R
P
K = P
IN
DRIVER
SW
IN
COIL
IN
= P
= P
= 1.6 + 2 x (0.015) x (95) + 155 x ((0.025 + 0.11 + 0.05 + 8)/8)
= 166.7W
= 1 . 6 + 2 . 8 5 + 1 6 2
= 2 x (0.015) x Q
(per channel) is approximated by:
OUT
OUT
= Resistance of the output filter inductor (typically around 50m:)
DRIVER
DRIVER
= Power dissipated in the TA0103A = 1.6W/channel
/P
/P
IN
IN
= 155/166.7 = 93%
+ P
+ P
SW
SW
+ P
+ P
g
DS (ON)
(Q
OUT
OUT
g
is the gate charge of M, in nano-coulombs)
((R
((R
of 0.065: was multiplied by a factor of 1.7 to obtain R
S
S
+ R
+ R
ON
ON
+ R
+ R
COIL
COIL
+ R
+ R
L
L
)/R
)/R
DS (ON)
T r i p a t h T e c h n o l o g y , I n c . - T e c h n i c a l I n f o r m a t i o n
L
L
)
)
2
2
typically increases by a factor of 1.7
2
TA0103 – Rev 3.3/06.00
SW
. For a TA0103A
ON
in order
ON
S
, of
of