Introduction to Intersil Analog Signal Path Products
Welcome to Intersil’s introductory course on analog electronics. This course is designed to provide a technical overview of Intersil analog signal path products.
The subjects we will cover in this presentation include amplifiers, voltage references, digitally controlled potentiometers (DCPs), interface ICs, data converters, switches and multiplexers, and real-time clocks.
Overview of Intersil Signal Path Products
This diagram shows the overview of the various products we will cover in this training module. As can be seen, Intersil offers a wide range of precision analog products which are specifically targeted at systems requiring very high performance and high precision. It is this portfolio of precision technology which makes Intersil a leader in the precision analog IC marketplace today.
Intersil’s precision op amp portfolio delivers the best performing amplifiers in achieving low offset voltages, low noise and overall higher performance at low power.
Amplifiers are used for a variety of applications. They are often used to convert analog “real” world signals, into a digital domain signal so that a microprocessor can process it. In the block diagram above, a multiplexer inputs a signal to an amplifier where an analog signal is conditioned. This is known as analog signal processing. Analog processing can include filtering, amplification, buffering, etc. Once the signal is conditioned, the signal is then sent to an ADC converter and finally to the microprocessor.
Amplifiers are also normally used for the amplification of both AC and DC signals, buffering with high input impedance, to the low output impedance necessary for driving ADCs’ driving signals, along with gain, level shifting, and active filters. Amplifiers are also often used for current-to-voltage and voltage-to-current conversions, along with mathematical operations such as summing, subtracting two or more signals, integration, and differentiation.
Ideal Op Amp Characteristics
The ideal operational amplifier’s characteristics include infinite input impedance, zero output impedance, infinite bandwidth, infinite open loop gain, and no DC errors. This unfortunately is never really the case. In the next few slides I will discuss the real world operational amplifier specifications that could effect the performance in an analog system.
Offset Voltage (VOS)
The input offset voltage is the mismatch of two transistors in the input pair. This causes small DC offset voltage errors to occur within the input of the op amp. Because of the op amp’s very large open loop gain, any inaccuracy in the voltages on the inputs is amplified several hundred times which can greatly effect the amplifier’s output.
Offset Voltage Drift (TCVOS)
Another variable of voltage offset is temperature. Every semiconductor device has a temperature coefficient (TC). This TC must be considered when calculating gain as a function of temperature.
Input Bias Current (IB) & Input Offset Current (IOS)
Another important mismatch in the operational amplification’s characteristics is the input bias current. If the bias current has leakage due to the transistors as described earlier, this is a major contributor of errors. Bipolar transistors have larger leakage in the nA range. CMOS/JFET transistors are usually in the pA range.
Typical Sensor System Block Diagram
An example where VOS could be critical is in a sensor system. This pressure sensor application uses a very small voltage as the sensor output and you never want your error from the VOS to be larger than your sensor signal. Therefore in this application, it is recommended to use an amplifier with the smallest offset possible.
An example of where TCVOS can be critical could be in the calibration of a system. Sometimes due to temperature, a DC offset voltage error can cause a voltage error throughout the digital processor which could cause an error on the output of the ADC.
Unfortunately, it can be very difficult to account for temperature drift. So if TCVOS is very important in a particular application, there are other configurations which do a better job in handling VOS.
Intersil Op Amp Product Families
At Intersil we have two families of op amps. One is high speed and the other is precision. Fundamentally, if the speed of an op amp is greater than 50MHz, then it belongs to the high-speed category.
The high-speed op amp family includes rail-to-rail voltage feedback amplifier, current feedback amplifier, slew enhanced, high voltage, fixed gain, differential drivers/receivers, and fully differential amplifier.
Meanwhile, chopper or zero-drift amps, micropower precision op amps (1.8V to 5V), high voltage precision op amps (2.5V to 40V) low cost op amps etc. belong to the precision op amp family.
Intersil also provides highly integrated amplifiers, also known as instrumentation amplifiers or in-amps.
There are several classic in-amp configurations using single, dual and triple op amps as shown.
With experience, these in-amps can be built using op amps, but there are many trade offs.
To help customers in their design, Intersil offers several in-amps that offer high precision and accuracy. Even a programmable gain in-amp to change the gains on the fly.
In addition, Intersil also offers dedicated current sense application—both analog output and digital output (otherwise known as digital power monitor or DPM) are available.
Intersil offers a wide range of precision series voltage references in both FGA™ and Band-gap technology.
Floating Gate Array (FGA) References
Intersil offers two types of series voltage references: floating gate array (FGA) and Band-gap references.
The first is the floating gate array, a proprietary technology from Intersil. The FGA reference uses the same technology as an EEPROM cell to maintain a precise voltage with very low supply current. The gate of an NMOS can be charged and discharged by increasing the voltage on VE or VP. If the voltages are set at the right level and timed correctly, a precise voltage is set on the gate. Because the gate is isolated by oxide on all sides, it is referred to as a floating gate and can hold a charge almost constant for many years. The NMOS (reference amp) is part of the amplifier circuit, which provides the desired reference voltage.
A band-gap voltage reference is a temperature independent voltage reference. It produces a fixed output voltage with power supply variations, temperature changes and the loading on the device. The output voltage is a function of VCTAT which is voltage vs. temperature (K) and VPTAT which is a function of the transistor voltage (Cx).
Voltage Reference Products by Type
Intersil offers several products that use both the floating gate array and band-gap technology.
The ISL21009 is a good very accurate FGA type voltage reference used in many applications.
Intersil also offers the lowest power precision voltage reference, the ISL60002. It is a great choice for portable, wearable or remote sensing applications.
Band-gap references are a good choice and typically used in the industrial/instrumentation application space.
Voltage References Selection Criteria
One of the most important criteria in selecting any voltage reference is its voltage precision or accuracy. This is critical for precision measurements such as a digital multimeter and other similar test equipment.
Note: Accuracy is not as important for ratiometric applications and self-calibration systems.
Another important criteria is drift versus temperature (ppm/°C or µV/°C), over time (ppm, ppm/√(1000hr)).
Also assembly shift, package stress (mechanical stress), IC layout, etc.
An extremely important concern on any noise source is noise. Particularly low frequency noise is very difficult to filter out.
Other important criteria include power consumption, the actual supply voltage to which you are interfacing and of course price.
Voltage Reference Design
Also, please do not forget filters on the output to reduce noise. And, be aware of transient response time.
Keep the voltage reference design in a stable region of operation, be especially mindful of capacitive loads.
And, keep the signal in phase for ratiometric designs such as sensors, as the voltage reference signal must reach the ADC at the same time as the sensor to eliminate undesired effects.
Intersil offers low-to-high resolution digital potentiometers in single, dual and quad configurations. Available in both linear and non-linear tapers, these digital potentiometers replace mechanical potentiometers and trim resistors in applications where digital control allows microprocessor interfacing and extended functionality.
Digitally Controlled Potentiometer
What is a DCP? If you are familiar with the traditional mechanical potentiometer, the DCP behaves similarly, but allows for much more flexibility and dependability.
Each DCP has total resistance just like a mechanical potentiometer. This is the maximum resistance of the part.
The total resistance is divided into equal segments referred to as “taps.” By increasing the number of taps in a part, the resolution increases, similar to increasing the number of speed settings available on a small motor. The user can then “tap” into the DCP at any of these joints to vary their output value through the use of the wiper (Vw/Rw), which can be compared to stopping the control of the motor dial to your chosen intensity.
Key Applications - DCPs are Multimarket Products
The applications for digital potentiometers are plentiful as adjustments are needed everywhere, whether they are being used to fix a problem, add precision and flexibility on the manufacturers’ side or to provide a value-added feature for the end user.
To name a few applications, digital potentiometers are sold in the industrial market primarily to set specific values in factory test systems so that recalibration is not needed. In the medical market, digital potentiometers can be used to control the drip on an infusion pump and adjust or maintain accuracy on other machines or systems. They are also found in base stations - used to set the optimum bias point for the FET gate voltage of the RF power amps.
Military systems also use digital potentiometers for calibration or bias control in radar and guidance systems. They are also used inside consumer products to adjust volume and tone control, and used in the production line to adjust and calibrate the Vcom in LCD panel displays to essentially reduce flicker.
Questions to Ask Your Customer
It is important to understand the customer’s requirements, and is easy to select the right DCP once this is known. There are five simple questions that need to be asked: whether they need memory, what resolution is needed, what interface they are using, what voltage range they need across the terminals, and the temperature range.
Remember, many of these specs are not exact. For example, if the customer would like a 64-tap device. Sometimes, they will be able to live with a 32-tap device, and reduce the voltage across the terminals. In addition, it might be cheaper for them to offer a 128-tap device, because this part may be on a new process. You can usually offer a higher resolution device, but it takes more convincing to offer a lower resolution device.
As far as interface, this is usually a critical parameter. However, there is the occasion where a customer wants to use SPI, and you can convince them that the U/D will also work in the application.
Temperature range is easy. All of our parts are offered up to 85 °C, and the newer devices operate up to 125 °C. Intersil was the first company that offered a non-volatile device that operates up to 125 °C, ideal for industrial applications.
DCP Architecture – Interface Types
Intersil’s digital potentiometers offer three options for the programming interface.
The first type, Type 1, is a serial bus interface. Intersil offers two popular interfaces, namely 2-wire or I2C and SPI bus. These interfaces require either a 2- or 3-pin interface to support byte level commands that are fed serially to the potentiometer on a data to clock format. The SDA and SI/SO pins are serial data pins used for data transfers; while the SCL and SCK are clock pins.
Both of these devices support slave addresses (e.g. A0:Ai pins) that allow for many devices or potentiometers to be used in parallel on the same physical interconnect. Both of these devices are heavily supported by the industry and common to many microcontroller, microprocessor and similar control devices.
Type 2, is primarily a step up/down counter interface (Intersil calls it a 3-wire interface). Basically, three pins are required; the U/D pin tells the potentiometer to increment or decrement; the INC pin tells the wiper when to move, and the CS pin is a chip select pin to enable/disable the chip. Note that a push pot style interface can be used with these devices with some external circuits.
The last interface, Type 3, is a push pot style interface. This interface is ideally suited for mechanical dip switches and requires very few external components.
Large Selection of Digital Potentiometers
As can be seen in this slide, Intersil offers a wide selection of digital potentiometers products from single to quad, ranging from single to quad r16 taps all the way to 1024-taps.
Intersil offers dual protocol transceivers, voltage level translators, I2C buffers, wide operating voltage range RS-485/422 type devices with the highest noise immunity and ESD protection in small packages that are available to support high-speed data transfer with a variety of configurations to fit your application.
RS-232 Wired Communication Standard
RS-232 is a legacy wired communication standard that uses single-ended signaling, for distances up to about 100ft.
Its ±5V levels provide better noise immunity than standard CMOS or TTL levels.
Our RS-232 ICs generate ±5V output supplies from single input supplies as low as 3.3V. They use charge pumps that double and then invert the Vcc, so with a 3.3V Vcc you get output supplies of about ±6V.
We offer compliant data rates up to 250kbps, and noncompliant data rates up to 1Mbps. The only compliance issue is not meeting the RS-232 max SR limitation of 30V/µs. There is no way to get 1Mbps with this limitation, so we increase SR to a max of 150V/µs.
RS-232 is for point-to-point communication, meaning that 1 Tx talks to only 1 Rx over the same wire.
Reasons Applications Still Use RS-232
The demise of RS-232 has been predicted for over a decade, so with USB, thunderbolt, etc. why does it keep hanging on?
The main reasons are that it is simple to use, well understood and cheap to implement.
The slow edge rates and short transmission distances eliminate transmission line effects, so there is no worry about terminations. The standard wire cables are cheaper than twisted pair or coax, and it takes only three wires to make a bidirectional interface. An RS-232 link doesn’t require the purchase of any IP, nor are there device registration fees.
So, RS-232 is still fine for apps where data exchange is intermittent, and when there aren’t large amounts of data to transmit. Application examples are POS bar code scanners and flat panel TVs.
Defining RS-485 and RS-422
RS-485 and RS-422 are both wired communication standards that are defined to handle long and noisy runs. Differential signaling and a wide CMR allow the receiver to reject noise picked up in noisy environments. The large 1.5V driver differential output voltage, coupled with a very sensitive receiver that detects signals as small as ±200mV, allows the network to handle the attenuation from long cables. Further help is provided by a ground return, which minimizes the CMR difference between distant nodes.
RS-485 and RS-422 are also relatively fast, with the standard allowing 10Mbps data rates. In reality, there are available devices with data rates up to 100Mbps.
An important point here is that data rate is inversely proportional to transmission length. Data rates are limited to about 100kbps to achieve 4,000ft, and at 40Mbps type rates the allowed distance drops to a few hundred feet.
There are some major differences between RS-485 and RS-422. RS-485 allows 32 devices on the bus, in any combination of receivers and transmitters, while RS-422 allows only one driver and up to 10 receivers. The one driver limitation means that an RS-422 bus is unidirectional, while RS-485 can communicate bidirectionally over a single bus. Bidirectional communication requires a termination at both ends of the bus, while RS-422 allows only one term. Finally, RS-485 requires a wider CMR of -7V to +12V.
A major application for RS-422 is as an RS-232 extension cord. RS-232 is converted to RS-422 at both cable ends, in order to connect two RS-232 devices that are far apart.
Single Transmit and Receive RS-485/422
So what are RS-485/RS-422 drivers and receivers and why are they important?
In an industrial environment digital data sent from industrial process control systems for example are sent through long cables and depending on the cable type and length the data could be so corrupted and distorted that the signal reaching the other receiver may actually be unrecognizable.
RS-485 and RS-422 drivers and receivers are used in repeaters in order to reconstruct and buffer the data signals in order to make sure the signals make it to the receivers in the correct format.
RS-485/RS-422 define the signal conditioning as well as the data rate, voltage level, and other conditions such as fault conditions.
Intersil offers single versions of both transmitter and receiver RS-485/RS-422 products.
Devices allow on bus = 256
Data rates (Mbps) = 20
Vcc range = 3.3V – 5.5V
Quad Transmitter/Receiver RS-485/RS-422
Intersil also offers quad transmitter and receiver type products.
The data rates range from 20 to 80Mbps with individual gate or group enable control functions.
Another great feature that Intersil provides in a complete mix of the RS-485/RS-422 and the older RS-232 legacy type transmitter and receiver products.
Number of ports = 1 or 2
Number on TX/Rx per port = 1/1 RS-485/422, 2/2 RS-232
Overvoltage Protected RS-485/422 Family
Since RS-485/RS-422 are often used in industrial environments where high voltage is often present, Intersil’s has a product family with built in 15kV ESD protection. With this built in feature, the cost of designing and procuring primary protection on the driver/receiver’s front end is greatly reduced.
Enhanced ESD and Noise Immunity
With enhanced ESD and noise immunity, Intersil’s RS-485/RS-422 drivers and receivers are used in many industrial environments where enhanced protection and multiple transmitters and receivers and required.
Intersil's data converter products include high-speed and precision analog-to-digital converters and high-speed digital-to-analog converter products.
D/A and A/D Converter Inputs and Outputs
Data converters change an analog signal to a signal compatible to the digital domain space and back again. This is accomplished by using an ADC and then a DAC.
Analog-to-digital converters or ADCs for short measure an input signal based on a comparison to a reference voltage and deliver a digital result at their outputs. If the input signal is higher than the reference voltage the signal is sent through the ADC as a valid input signal.
Digital-to-analog converters or DACs for short are the opposite of ADCs, where they generate an analog output in response to a digital input word, which is the measured as a fraction of a known reference.
The output range (in the case of a D/A converter) or input range (in the case of a A/D converter) is divided into 2 to the N bits, where N is the resolution of the converter.
ADCs and DACs are used mostly in measurement equipment where exact digital and analog measurements are required.
Focusing on the A/D converter, we can see that before routing the signal to the converter, the input filter removes any noise picked up by the sensor. Operating at a known sampling rate, the converter digitizes the signal and generates a stream of data - corresponding to the resolution of the converter. It is easy to see that a 3-bit converter does a pretty rough job on the smooth analog input signal.
Here are the most popular types of A/D converter architectures. For the purposes of this training module which relates to Intersil’s precision converter products, we will focus on the Delta-Sigma and Successive Approximation types of ADC architectures.
Intersil does not support Pipelined or Flash ADC architectures, as Delta-Sigma and Successive Approximation architectures are more commonly used today.
Delta-Sigma ADCs utilize sophisticated digital filtering architectures implemented in fine-line CMOS processes to achieve low noise performance, and thus very high measurement accuracy. By taking a very large number of samples and mathematically averaging the result over a period of time, we can achieve very high resolution, with absolutely dependable results independent of common errors such as amplifier gain and offset drift.
Another benefit of the high sample rate is that we can take advantage of the higher clock rate and “push” the noise up to a higher frequency where it is easier to remove with a low-pass filter.
But the biggest advantage of this approach is that we can perform the majority of the filtering and error correction of the input signal in the digital domain, where filtering performance is based on fixed, absolutely repeatable mathematical operations, and not error-prone, noise-sensitive analog circuits.
Another common and very important feature of Delta-Sigma converters is an integrated low-noise input buffer amplifier with the high gain appropriate to low-level sensors. These circuits are among the most demanding designs of all, and having them integrated onboard offers numerous advantages for cost and space savings, and optimal elimination of noise and error sources.
Successive Approximation (SAR) ADCs
Compared to sophisticated oversampling converters, Successive Approximation ADCs are the basic, long-proven workhorses of the industrial world. Their simple architectures and high bandwidth make them the converter of choice in most medium-bandwidth signal acquisition applications. When correctly designed and compensated, they are dependable, robust and provide good accuracy at relatively low cost.
Intersil's broad portfolio of analog switches and multiplexers provide excellent performance across a wide input voltage range. Products include 40V operation down to low voltage USB switching.
There are many definitions for what is defined as a switch versus a MUX. This slide defines the switch/mux and crosspoint definitions.
SPST – Single Pole Single Throw
DPST – Double Pole Single Throw
DPDT – Double Pole Double Throw
Low Voltage Sub 0.5W Switch Overview
Intersil offers a low voltage low rds on family of switches with 9kV ESD voltage capability. This product family, due to the low rds on, is targeted for the handheld market.
Low Voltage Analog Switch
As can be seen from the table on this slide, Intersil has several single (SPST) and dual (DPDT) analog switch products to fit most applications. The current table only shows low voltage analog switches. Medium and high voltage analog switches are also available.
Intersil’s family of real-time clock products offers a wide variety of useful industry standard functions and features covering basic low-cost clock and calendar RTCs, feature-rich RTCs including supervisory functions and EEPROM memory.
Real-time clock devices are used to improve a product’s time keeping accuracy. RTCs also provide many features associated with specific applications such as tamper detection of remote devices.
The real-time clock tracks time with separate registers for hours, minutes and seconds. The device has calendar registers for date, month, year, and day of the week.
Many customers want additional features such as battery backup capability, memory and event tracking.
Intersil RTCs require a crystal to provide a timing signal which is used by the RTC to calculate the time and date.
The time/date information of all Intersil RTCs is provided to the system microcontroller via an I2C Interface.
Real-Time Clock Application
In this training module, the real-time clock provides critical real-time information to all kinds of systems. Any system that needs time information, will require a real-time clock.
High Accuracy Real-Time Clocks
Intersil offers a high accuracy RTC family. This family includes the ISL12022/23 and ISL12020M/22M. The M stands for module, which means the crystal is built inside the package. It is good for utility meters, medical devices and GPS devices, or any device that needs accurate time information.
Applications for Real-Time Clocks
Ideal applications for real-time clocks include the following.
Used to collect data at specified time intervals.
Data collection terminal, smart card reader, which requires the real-time clock to keep track of the day and time of certain tasks taking place.
In today’s telecommunication systems such as a LAN, FAX or router, timekeeping and security is an important issue. For example, a FAX machine uses a real-time clock to stamp the time when a document was sent and received. This timekeeping provides the user the ability to proof the delivery of the documents. In conjunction with the RTC and the EEPROM, critical system data can be stored in the non-volatile memory array. After a system power fails, all configuration data can auto recalled from the EEPROM.
RTCs could be used with memory devices to alert IT professionals when it is time to provide the weekly or monthly maintenance of system servers.
It is our hope that you now have a basic understanding of the feature and benefits of Intersil precision analog products. Thank you for listening to this training module.