Microchip Technology Photodiode PGAPICtail, Руководство пользователя

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PHOTODIODE PGA PICTAIL™
DAUGHTER BOARD USER’S GUIDE

2004 Microchip Technology Inc. DS51514A-page 17
Appendix A. Schematic and Layouts
A.1 INTRODUCTION
This appendix contains the schematics and layouts for the Photodiode PGA PICtail™
Daughter Board.
The MCP6SX2-PICTLPD Demonstration Board is constructed using a two-layer
Printed Circuit Board (PCB). The top layer is for components and traces. The bottom
layer is the ground plane.
Information on this board includes:
• Board Schematic
• Board - Top Silk-Screen And Metal Layers
• Board - Top Metal Layer
• Board - Bottom Metal Layer
A.2 DEMONSTRATION BOARD DESCRIPTION
A simplified schematic is shown in Figure 1.3, with the complete schematic being pre-
sented in A.4 “Board Schematic”. D
1
is the photodiode that converts light into current.
Op amp U
1
and resistor R
1
convert the current into a voltage; they form a transimped-
ance amplifier. Capacitor C
1
stabilizes the transimpedance amplifier.
R
2
and C
2
filter the transimpedance amplifier’s output to reduce noise. They also act
as an anti-aliasing filter for the ADC. The voltage V
OUT
appears at this filter’s output.
The MCP6SX2 Programmable Gain Amplifier (PGA) can be either the MCP6S22 or the
MCP6S92. The PGA gains V
OUT
up to produce the ADC’s input voltage V
PGA
. It also
provides the capability to send another input to the ADC. It receives commands from
the PIC16F684 via the SPI™ serial bus.
The PIC16F684 is on the Signal Analysis PICtail Daughter Board (PIC16F684) and
provides an internal 10-bit ADC for measuring V
OUT
. It also controls the PGA via the
SPI serial interface.
The firmware on the PIC16F684 works with the PICkit 1 Signal Analysis PC program
(see Section 1.4.6 “Firmware for the Signal Analysis PICtail Daughter Board”).
This is a two-layer board. It has a solid ground plane on the bottom layer to minimize
EMC issues, and routes the traces in the top layer. The complete schematic is in
Sections A.4 “Board Schematic”; the board layer plots in A.5 “Board - Top
Silk-Screen And Metal Layers”, A.6 “Board - Top Metal Layer”, A.7 “Board - Bot-
tom Metal Layer” and Appendix B. Bill-Of-Materials (BOM). The Gerber files for this
board are available on the Microchip web site (www.microchip.com) and are contained
in the zip file
00951.zip
.