ID A14C: Getting Optimal Performance from your ADC

35 Pages·2010·1.76 MB·English

ID A14C: Getting Optimal Performance
from your ADC
Renesas Electronics America Inc.
Jim Page
Senior Applications Engineer
12 October 2010
Version: 1.1
In the market place today the myth about embedded Ethernet is that it very hard to achieve.
In this presentation and lab, I will show you that Open-Source TCP/IP stacks with freely available tools
are now true enablers for less costly embedded Ethernet products.
1
Jim Page
(cid:1) Senior Applications Engineer
(cid:2) 14 years experience with variety of Renesas tools
(cid:2) R8C/M16C/740 series processor primary support
(cid:2) Member of Renesas Technical Support Staff for web customer support
(cid:2) Key support and development role for several successful projects
being used in-field today using broad variety of Renesas and 3rd party
tools
(cid:1) B.S. EET from Western Carolina University
(cid:2) Go Catamounts!!
(cid:1) Expert in USB and other serial technologies
(cid:2) Co-patent holder/developer of original Renesas Flash-Over-USB
technology
(cid:2) Expert in I2C, SPI, and other serial protocol interfaces using Renesas
MCUs
2
Renesas Technology and Solution Portfolio
Microcontrollers
& Microprocessors
#1 Market share
worldwide *
SSoolluuttiioonnss
ffoorr
IInnnnoovvaattiioonn Analog and
ASIC, ASSP
Power Devices
& Memory
#1 Market share
Advanced and
in low-voltage
proven technologies
MOSFET**
* MCU: 31% revenue
basis from Gartner
"Semiconductor
Applications Worldwide
Annual Market Share:
Database" 25
March 2010
**Power MOSFET: 17.1%
on unit basis from
Marketing Eye 2009
(17.1% on unit basis).
In the session 110C, Renesas Next Generation Microcontroller andMicroprocessor Technology
Roadmap, Ritesh Tyagi introduces this high level image of where the Renesas Products fit. The big
picture.
Renesas Technology and Solution Portfolio
Microcontrollers
& Microprocessors
#1 Market share
worldwide *
SSoolluuttiioonnss
ffoorr
IInnnnoovvaattiioonn
ASIC, ASSP Analog and
& Memory Power Devices
Advanced and #1 Market share
proven technologies in low-voltage
MOSFET**
* MCU: 31% revenue
basis from Gartner
"Semiconductor
Applications Worldwide
Annual Market Share:
Database" 25
March 2010
**Power MOSFET: 17.1%
on unit basis from
Marketing Eye 2009
(17.1% on unit basis).
4
This is where our session, A14C, is focused within the ‘Big picture of Renesas Products’, Microcontroller
and Microprocessors.
Microcontroller and Microprocessor Line-up
Superscalar, MMU, Multimedia (cid:3)Up to 1200 DMIPS, 45, 65 & 90nm process
(cid:3)Video and audio processing on Linux
(cid:3)Server, Industrial & Automotive
(cid:3)Up to 500 DMIPS, 150 & 90nm process
High Performance CPU, Low Power
(cid:3)600uA/MHz, 1.5 uA standby
(cid:3)Medical, Automotive & Industrial
(cid:3)Up to 165 DMIPS, 90nm process
High Performance CPU, FPU, DSC (cid:3)500uA/MHz, 2.5 uA standby
(cid:3)Ethernet, CAN, USB, Motor Control, TFT Display
(cid:3)Legacy Cores
(cid:3)Next-generation migration to RX
General Purpose Ultra Low Power Embedded Security
(cid:3)Up to 10 DMIPS, 130nm process (cid:3)Up to 25 DMIPS, 150nm process (cid:3)Up to 25 DMIPS, 180, 90nm process
(cid:3)350 uA/MHz, 1uA standby (cid:3)190 uA/MHz, 0.3uA standby (cid:3)1mA/MHz, 100uA standby
(cid:3)Capacitive touch (cid:3)Application-specific integration (cid:3)Crypto engine, Hardware security
5
Here are the MCU and MPU Product Lines, I am not going to cover any specific information on these
families, but rather I want to show you where this session is focused
Microcontroller and Microprocessor Line-up
Superscalar, MMU, Multimedia (cid:3)Up to 1200 DMIPS, 45, 65 & 90nm process
(cid:3)Video and audio processing on Linux
(cid:3)Server, Industrial & Automotive
(cid:3)Up to 500 DMIPS, 150 & 90nm process
High Performance CPU, Low Power
(cid:3)600uA/MHz, 1.5 uA standby
(cid:3)Medical, Automotive & Industrial
(cid:3)Up to 165 DMIPS, 90nm process
High Performance CPU, FPU, DSC (cid:3)500uA/MHz, 2.5 uA standby
(cid:3)Ethernet, CAN, USB, Motor Control, TFT Display
(cid:3)Legacy Cores
(cid:3)Next-generation migration to RX
General Purpose Ultra Low Power Embedded Security
(cid:3)Up to 10 DMIPS, 130nm process (cid:3)Up to 25 DMIPS, 150nm process (cid:3)Up to 25 DMIPS, 180, 90nm process
(cid:3)350 uA/MHz, 1uA standby (cid:3)190 uA/MHz, 0.3uA standby (cid:3)1mA/MHz, 100uA standby
(cid:3)Capacitive touch (cid:3)Application-specific integration (cid:3)Crypto engine, Hardware security
6
A/D converters are in all product families. Well, maybe not security, but the rest.
Innovations in Analog
7
We’ve come a long way in analog. As this picture eloquently depicts, man’s first foray into analog and
understanding how analog works is filled with mystery, ‘black magic’and other issues that make
dealing with analog signals difficult to understand at times.
7
Innovations in Analog – Voice Recognition
8
Didja ever notice that Captain Kirk never had to fuss with a mouse or keyboard to communicate with the
computer on the Star Trek? He simply spoke direct commands at the machine, and the computer
complied.
Simply put, voice recognition softwareallows you to speak commands to a computer rather than use a
mouse or keyboard. Though it may seem like a futuristic notion, voice computing or speech
recognition has been around for over a decade, and is still a rapidly evolving technology.
The Microsoft Sync System is a perfect example that is available in Ford brand vehicles. Even though
it's not used by many on their home PCs, you probably have already encountered this type of data
input. This technology depends greatly on interfacing a digital domain to the analog world. As such
understanding analog to digital conversion, it’s issues and techniques is key to many embedded
developments
In this course we’ll delve into the world of ADCs, their implementation, and othertopics to help you, the
embedded designer, get the most out of using the highly important interface products
8
Agenda
(cid:1) Successive Approximation and Delta-Sigma Converters
(cid:2) Basic Concepts
(cid:2) Advantages and Disadvantages
(cid:1) ADC Key Terms and Concepts
(cid:1) Source resistance limitations
(cid:1) Discussions of how often to sample
9
During this presentation we are going to look at a few basic application level ADC considerations.
These include
The successive approximation and Delta-Sigma converter ADC concepts. These are the two most
common ADCs that are found on MCUs today. We will look at both the basic diagram of these
devices and discuss the pros and cons of the two types
After looking at two fundamental types of ADCs we will then discuss basic concepts of ADCs including,
error terms, some basic facts pertaining to a 10 bit ADC and the concept of ratio-metric vs non-
ratiometric measurements
Next we will discuss the effect of source resistance on the accuracy of the measurement and some
options to improve the accuracy
Finally we will disccuss selecting the sampling rate of the signal based on the application
9
Successive Approximation (SAR) ADC
ADC Register
01 1 0 1 1 0 0 1 0 0
Vref
DAC (R2R Ladder)
AVss
AN0 Comparator
AN1
AN2
AN3
AN4
AN5
AN6
AN7
Sample and
Hold Circuit
Input Analog
Mux
10
Here is the block diagram of a successive approximation ADC.
You can see that this ADC has 8 channels muxed together. A “snapshot”of the analog input is then
grabbed byt the sample and hold circuit. This captured signal is then applied to a comparator along with
the output of and digital-to-analog converter which is typically constructed using an R2R ladder. The
input to the DAC is adjust one bit at a time, starting with the MSB, and at each step the output of the
comparator is used to see if this made the output of the DAC larger than the sampled voltage or not. If it
larger the bit is set back to 0, if not it is left as a one. Then the next least significant bit is tested. After
each bit is tested the equivalent digital value of the analog input is moved to the ADC register to be read.
Note that the R2R ladder is fed by Vref. This is important to remember because the R2R ladder does
draw current, often on the order of a mA, when a conversion is in progress. The reference must be able
to supply this current without it affecting the voltage from the reference or an error will be introduced.
Because of this you typically want to provide a good bypass circuit for Vref
10