Tripath Technology, Inc. - Technical Information
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To minimize noise pickup and minimize THD+N, RFBC (R106/R109) should be located as
close to the TA3020 as possible. Make sure that the routing of the high voltage feedback
lines is kept far away from the input op amps or significant noise coupling may occur. It is
best to shield the high voltage feedback lines by using a ground plane around these traces
as well as the input section.
CB (C111), CSW (C5) provides high frequency bypassing for the VN10 and bootstrap
supplies. Very high currents are present on these supplies.
In general, to enable placement as close to the TA3020, and minimize PCB parasitics, the capacitors
CFB, CB and CSW should be surface mount types, located on the “solder” side of the board.
Some components are not sensitive to location but are very sensitive to layout and trace routing.
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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 (L100).
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The output filter capacitor, CO (C108), and zobel capacitor, CZ (C109), should be star
connected with the load return. The output ground feedback signal should be taken from
this star point.
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The modulator feedback resistors, RFBA (R105/R108) and RFBB (R107/R110), should all be
grounded and attached to 5V together. These connections will serve to minimize common
mode noise via the differential feedback.
The feedback signals that come directly from the output inductors are high voltage and high
frequency in nature. If they are routed close to the input nodes, INV1 and INV2, the high
impedance inverting opamp pins will pick up noise. This coupling will result in significant
background noise, especially when the input is AC coupled to ground, or an external
source such as a CD player or signal generator is connected. Thus, care should be taken
such that the feedback lines are not routed near any of the input section.
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To minimize the possibility of any noise pickup, the trace lengths of INV1 and INV2 should
be kept as short as possible. This is most easily accomplished by locating the input
resistors, RI (R100), and the input stage feedback resistors, RF (R101), as close to the
TA3020 as possible. In addition, the offset trim resistor, ROFB (R103), which connects to
either INV1, or INV2, should be located close to the TA3020 input section.
Performing Measurements on the EB-TA3020
The TA3020 operates by generating a high frequency switching signal based on the audio input. This
signal is sent through a low-pass filter that recovers an amplified version of the audio input. The
frequency of the switching pattern is spread spectrum in nature and typically varies between 100kHz and
1MHz, which is well above the 20Hz – 20kHz audio band. The pattern itself does not alter or distort the
audio input signal, but it does introduce some inaudible components.
The measurements of certain performance parameters, particularly noise related specifications such as
THD+N, are significantly affected by the design of the low-pass filter used on the output as well as the
bandwidth setting of the measurement instrument used. Unless the filter has a very sharp roll-off just
beyond the audio band or the bandwidth of the measurement instrument is limited, some of the inaudible
noise components introduced by the TA3020 amplifier switching pattern will degrade the measurement.
One feature of the TA3020 is that it does 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
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RB-TA3020, Rev. 3.0/03.02
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
