TA3020 Ver la hoja de datos (PDF) - Unspecified
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TA3020 Datasheet PDF : 27 Pages
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Tripath Technology, Inc. - Technical Information
Input Stage Design
The TA3020 input stage is configured as an inverting amplifier, allowing the system designer flexibility in setting
the input stage gain and frequency response. Figure 2 shows a typical application where the input stage is a
constant gain inverting amplifier. The input stage gain should be set so that the maximum input signal level will
drive the input stage output to 4Vpp.
The gain of the input stage, above the low frequency high pass filter point, is that of a simple inverting amplifier:
A VINPUTSTAG E = − R F
RI
INPUT1
RF
CI
RI
Figure 2: Input Stage
OAOUT1
TA3020
V5
INV1
INPUT2
RF
CI
RI
BIASCAP
AGND
V5
+
INV2
-
OAOUT2
AGND
Input Capacitor Selection
CIN can be calculated once a value for RIN has been determined. CIN and RIN determine the input low-frequency
pole. Typically this pole is set at 10Hz. CIN is calculated according to:
CIN = 1 / (2π x FP x RIN)
where: RIN = Input resistor value in ohms
FP = Input low frequency pole (typically 10Hz)
Modulator Feedback Design
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 voltages for the power stage. Depending on the maximum supply voltage, the feedback ratio will need
to be adjusted to maximize performance. The values of RFBA, 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 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.
Figure 3 shows how the feedback from the output of the amplifier is returned to the input of the modulator. The
input to the modulator (FBKOUT1/FBKGND1 for channel 1) can be viewed as inputs to an inverting differential
amplifier. RFBA and RFBB bias the feedback signal to approximately 2.5V and RFBC scales the large OUT1/OUT2
signal to down to 4Vpp.
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TA3020 – KL Rev. 3.0/09.03
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