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SI ARCADE SIGNAL PROCESSING PRINTED CIRCUIT BOARD (PCB) S780-100
Preamplifiers
The heart of the preamplifiers is U9 and U10, MAX410 low-noise low-distortion operational amplifiers. These
amplifiers with resistors R29, R31, R33 and capacitor C16 (U9), R30, R32, R34 and C17 (U10) form non-
inverting operational amplifier configurations with resistors R31 and R33 (U9) and R32 and R34 (U10), setting
the gain at approximately 42dB. Resistors R29 and R30 provide biasing current for the positive input of U9
and U10, respectively, while resistors R25 and R26 and capacitor C14 and R27 and R28 and capacitor C15
provide a 2.5VDC analog ground reference for U9 and U10, respectively. Capacitors C12 and C13 prevent
DC current from entering U9 and U10, respectively. Capacitors C16 and C17 provide high-frequency noise
filtering.
The second stage in this configuration provides approximately 10dB of gain. This section contains U12B and
U13B, OP213 dual low-noise amplifiers. Capacitors C19 and C21 provide DC decoupling. Resistors R35 and
R36 with capacitor C18 and resistors R37 and R38 with capacitor C20 form low-noise analog references for
U12 and U13 respectively. R57 and C24, which a resistor replaces, set the gain for U12B. RHAND, sits on
the pads for U11-pin 11 and U11-pin 13 and C26, which a resistor replaces, and sets the gain for U13B.
C23 and C25 decouple the output signals from the second amplifier stages to unity gain low-pass filters.
These filters contain op-amp U12A, resistors R39, R41, and capacitor C27 and op-amp U13A, resistors R40,
R42, and capacitor C28. Resistors R39, R40, R41, R42 set a fixed gain at 0dB. The outputs of U12A, pin 1,
and U13A, pin 1, are applied to low-pass anti-aliasing filters composed of R43 and capacitor C29 and R44 and
capacitor C31, respectively.
Analog to Digital (A/D) Converter
The analog to digital (A/D) converter section digitizes the analog outputs of the two preamplifier sections,
transforming the analog information to a digital representation for further processing by the DSP chip. U14, a
stereo 16-bit sigma delta A/D converter manufactured by Analog Devices, carries out the A/D conversion.
This converter accepts an analog signal and converts it to 16-bit signed digital words. Capacitor pairs C35, C38
and C36, C39 provide power supply filtering for the references. Capacitors C45, C46 provide power supply
filtering for the analog supply. Capacitors C47, C48, C49, and C50 provide power supply filtering for the digital
supply. Ferrite bead L1 and capacitors C33, C34 filter high-frequency signals from entering the A/D
converter's analog section. The DSP chip provides the sampling clock and is applied on pin 28 of U14. The
digitized data from the converter is serially output on pins 1, 2, 3, and 26.
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