Tripath Technology, Inc. - Technical Information
Some components are not sensitive to location but are very sensitive to layout and trace routing.
-
To maximize the damping factor and reduce distortion and noise, the modulator feedback
connections should be routed directly to the pins of the output inductors, LO.
-
The modulator feedback resistors should all be grounded together. These connections will
serve to minimize common mode noise via the differential feedback.
T K 2 0 7 0 G r o u n d i n g
Proper grounding techniques are required to maximize TK2070 functionality and performance.
Parametric parameters such as THD+N, noise floor and cross talk can be adversely affected if proper
grounding techniques are not implemented on the PCB layout. The following discussion highlights
some recommendations about grounding both with respect to the TK2070 as well as general “audio
system” design rules.
The TK2070 is divided into two sections: the input section, and the output (high power) section. On
the TK2070 evaluation board, the ground is also divided into distinct sections, one for the input and
one for the output. To minimize ground loops and keep the audio noise floor as low as possible, the
input and output ground must be only connected at a single point. Depending on the system design,
the single point connection may be in the form of a ferrite bead or a PCB trace.
Mo d u l ato r F eed b ack Desi g n
The modulator converts the signal from the input stage to the high-voltage output signal. The
optimum gain of the modulator is determined from the maximum allowable feedback level for the
modulator and maximum supply voltage for the power stage. Depending on the maximum supply
voltage, the feedback ratio will need to be adjusted to maximize performance. The values of RFBB
and RFBC (see explanation below) define the gain of the modulator. Once these values are chosen,
based on the maximum supply voltage, the gain of the modulator will be fixed even with as the supply
voltage fluctuates due to current draw.
For the best signal-to-noise ratio and lowest distortion, the maximum differential modulator feedback
voltage should be approximately 4Vpp. This will keep the gain of the modulator as low as possible
and still allow headroom so that the feedback signal does not clip the modulator feedback stage.
The modulator feedback resistors are:
RFBB = User specified; typically 1kΩ
VCC ∗ RFBB
RFBC =
− RFBB
2V
T K2070 Amp lifier Gain
The gain of the TK2070 is the product of the input stage gain and the modulator gain. Please refer to
the sections, Input Stage Design, and Modulator Feedback Design, for a complete explanation of how
to determine the external component values.
A
A
V TK2070 = AV INPUT STAGE * A
V
MODULATOR
R
R
F
I
R
FBC + RFBB
V TK2070
≈
R
FBB
13
TK2070 – MC/2.1/10-03
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
