- 您现在的位置：买卖IC网 > Sheet目录1227 > MA160011 (Microchip Technology)DAUGHTER BOARD PICDEM LCD 16F91X
MICROCHIP TECHNOLOGY’S MICROSOLUTIONS eNEWSLETTER - November 2005
Sometimes Noise Can Be Good
By Bonnie C. Baker, Microchip Technology Inc.
When I started to write this article someone saw the title
and asked, “You don’t have any kids, do you?” Well, I did
have the charge of children at one time in my life, but I
think people forget two things through their lives: extreme
pleasure and extreme pain. That’s why we keep going back
for more. This column is not about going back to painful
experiences such as a noisy circuit. Rather, it is about the
pleasure of tackling those difficult analog noise problems in
the digital domain.
final result. The accumulation of these samples takes
time. Finite Impulse Response (FIR) and Infinite Impulse
Response (IIR) digital filters are also well suited for this
task.
If you have the time, this sounds like a simple solution.
However, there is one more issue to consider before you
embrace this combination of analog with digital systems
in your circuit. You must know the complexion of your ADC
digital output over time. A histogram plot is an appropriate
We have all sought the perfect conversion in our mixed-signal tool to use when examining your digital code over time. The
circuits where the converter produces a repeatable, accurate histogram plot displays the number of occurrences of each
digital result every time. We use noise-reduction techniques code. For example, the histogram plot in Figure 1 shows
such as selecting low-noise devices, a careful layout and 1024 repetitive data samples from a 12-bit ADC (sample
analog filtering to remove undesirable signals. But, another rate = 20 ksps).
If you use a digital filter at the output of your ADC, you are
not relieved of the responsibility of knowing what kind of
resolution of your analog-to-digital conversion, but only if
way to approach noisy analog-to-digital conversion problems
is to “design” noise into your signal instead of out. For
instance, you can get 12-bit accuracy from a 12-bit converter
if you are diligent about applying low-noise strategies to
your circuit. As an alternative, you can allow a degree of
white noise into the circuit and follow the conversion with
a processor or controller digital filter. In this scenario,
your circuit is capable of producing 14-, 15- or even 16-bit
accuracy. If there is noise in your circuit, you can achieve
better resolution at the output of a digital filter by using
oversampling techniques.
For instance, if you use a simple rolling-average digital filter,
you can calculate the number of bits (N) that you will add to
your conversion resolution with this formula: #oversampled
data = 22N. If you want to increase your resolution from
11 bits to 14 bits, you need to accumulate and average
64 samples. Time is the primary tradeoff for this increase
in resolution. The rolling-average digital-filter algorithm
accumulates several samples in order to calculate the
If you want to successfully increase the resolution of your
converter, you need to ensure that the noise from the ADC
is gaussian in nature. In a histogram plot, gaussian noise
looks similar to a statistically normal distribution around a
center code. The data in Figure 1 does not follow the shape
of a normal distribution. The data in Figure 1 appears to
have a bi-modal response. In addition, the output mean of
this system should be 2236 instead of 2297. A digital filter
will not “fix” this data. The noise in this system originates
in an LED array. Poor layout and high currents through the
array make the noise on the board intolerable.
Figure 1: This histogram plot shows data from an ADC that is bimodal. It is difficult, if
not impossible, to apply digital filtering to this data to recover a digital code that actually
data you are producing. Digital filtering will improve the represents the input analog voltage accurately.
References
you are confident that the noise response of your data is “Mixed-Signal and DSP Design Techniques”, Walt Kester, Elsevier, 2003.
gaussian in nature.
For more information visit: www.microchip.com/LowPower
these I
about
er issu
Learn
ecemb
in the
LUTIO
Featured Product
The MCP3905/6 devices are energy metering ICs
that supply average active power information via
a pulse output with direct drive for mechanical
counters. They also include a higher-frequency
output that supplies instantanous power information
for calibration. The devices contain function blocks
specific for IEC energy meter compliance, such as
a no-load threshold and startup current.
The MCP3905/6 Energy Meter Reference Design
Printed Circuit Board (PCB) is used as a reference
design for single-phase, residential meters. The
MCP3905/6 Energy Meter Reference Design Kit
includes all necessary PCB circuits and layout tips for
IEC62053 and prior 1036/61036/687 active-energy
Cs
more e of
D NS!
m icroSO
For more information visit:
Microcontrollers ? Digital Signal Controllers ? Analog ? Serial EEPROMs
5
发布紧急采购，3分钟左右您将得到回复。
相关PDF资料
MA180021
MODULE PLUG-IN 18F87J50 FS USB
MA180024
MODULE PLUG-IN 18F46J50 FS USB
MA180028
MOD PLUG-IN PIC18F87K22 PIM
MA2-4-34-625-2-A32-7C
CIRCUIT BREAKER MAG 25A PANEL MT
MA240013
MODULE PLUG-IN PIC24 44-PIN
MA240017
MODULE PLUG-IN PIC24F16KA102 PIM
MA240021
MOD PLUG-IN PIC24FJ256GB210
MA240025-1
MOD PIM PIC24EP512GU810 GP
相关代理商/技术参数
MA160012
功能描述:子卡和OEM板 PIC16F193x 44P PIM For PIC18 Explorer RoHS:否 制造商:BeagleBoard by CircuitCo 产品:BeagleBone LCD4 Boards 用于:BeagleBone - BB-Bone - Open Source Development Kit
MA160012
制造商:Microchip Technology Inc 功能描述:PIC16F1937 Plug-in Module for PICDEM PIC
MA160014
功能描述:子卡和OEM板 PIC18LF45K22 Plug-In Module
RoHS:否 制造商:BeagleBoard by CircuitCo 产品:BeagleBone LCD4 Boards 用于:BeagleBone - BB-Bone - Open Source Development Kit
MA160015
功能描述:子卡和OEM板 PIC16LF1947 PIM RoHS:否 制造商:BeagleBoard by CircuitCo 产品:BeagleBone LCD4 Boards 用于:BeagleBone - BB-Bone - Open Source Development Kit
MA160016
功能描述:子卡和OEM板 PIC16F1947 PIM RoHS:否 制造商:BeagleBoard by CircuitCo 产品:BeagleBone LCD4 Boards 用于:BeagleBone - BB-Bone - Open Source Development Kit
MA161
制造商:Panasonic Industrial Company 功能描述:DIODE
MA16101BAN
制造商:MURATA 制造商全称:Murata Manufacturing Co., Ltd. 功能描述:HIGH FREQUENCY CERAMIC CAPACITORS
MA16101BBN
制造商:MURATA 制造商全称:Murata Manufacturing Co., Ltd. 功能描述:HIGH FREQUENCY CERAMIC CAPACITORS