MCP6021/1R/2/3/4
Separate digital from analog, low speed from high
speed and low power from high power. This will reduce
interference.
Keep sensitive traces short and straight. Separating
them from interfering components and traces. This is
especially important for high-frequency (low rise-time)
signals.
Sometimes it helps to place guard traces next to victim
traces. They should be on both sides of the victim
trace, and as close as possible. Connect the guard
trace to ground plane at both ends, and in the middle
for long traces.
Use coax cables (or low inductance wiring) to route
signal and power to and from the PCB.
4.11.2
OPTICAL DETECTOR AMPLIFIER
Figure 4-12 shows the MCP6021 op amp used as a
transimpedance amplifier in a photo detector circuit.
The photo detector looks like a capacitive current
source, so the 100 kΩ resistor gains the input signal to
a reasonable level. The 5.6 pF capacitor stabilizes this
circuit and produces a flat frequency response with a
bandwidth of 370 kHz.
5.6 pF
100 kΩ
100 pF
MCP6021
Photo
Detector
4.11
4.11.1
Typical Applications
A/D CONVERTER DRIVER AND
ANTI-ALIASING FILTER
V
DD
/2
Figure 4-11 shows a third-order Butterworth filter that
can be used as an A/D converter driver. It has a band-
width of 20 kHz and a reasonable step response. It will
work well for conversion rates of 80 ksps and greater (it
has 29 dB attenuation at 60 kHz).
FIGURE 4-12:
Transimpedance Amplifier
for an Optical Detector.
1.0 nF
8.45 kΩ 14.7 kΩ
1.2 nF
33.2 kΩ
100 pF
MCP602X
FIGURE 4-11:
A/D converter driver and
anti-aliasing filter with a 20 kHz cutoff frequency.
This filter can easily be adjusted to another bandwidth
by multiplying all capacitors by the same factor.
Alternatively, the resistors can all be scaled by another
common factor to adjust the bandwidth.
DS21685C-page 16
©
2006 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
