High Speed Amplifiers Part 3


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This training module introduces the packing improvement for high speed amplifiers and summary the performance & design considerations of high speed amplifiers

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  • Welcome to the training module on Analog Devices High Speed Amplifiers Part 3 . This training module introduces the packing improvement for high speed amplifiers and summary the performance & design considerations of high speed amplifiers.
  • Packaging plays a large role in high-speed applications. Smaller packages enable better performance at higher speeds, and compact layout. The low distortion pinout also provides compact layout, streamline signal flow, and lower distortion.
  • 04/14/11 The new high performance pin out or (low distortion pinout) from ADI is being used on many of their new high performance op amps. This pin out was introduced in 2003 with the release of the AD8099. These op amps are offered in two different packages: SOIC / LFCSP. The SOIC package is the standard 8 pin package that has been around for decades, but features a little twist, you can see they’ve added a dedicated feedback pin on pin 1 of the SOIC. This greatly simplifies PCB layouts. The pinout helps isolate the output from the load which improves the capacitor load stability. The LFCSP also has the feedback pin- here we have rotated the pins counter-clockwise by 1. This isolates the non-inverting input from the –Vs which is a source of 2 nd order harmonic distortion. Intersil has already released a product in the LFCSP package and pin out. These packages also feature an exposed thermal pad which helps get the heat out of the package, and keep the junction temperature down.
  • 04/14/11 This graph shows the same part (die) in both the SOIC and LFCSP package. As you can see, the part in the LFCSP package with the new pinout has ~14dB and better 2 nd HD at 10 MHz than the SOIC.
  • Here’s an example of a traditional SOIC package and layout. The Feedback path is routed around amplifier, which as we discussed earlier can introduce parasitic inductance and cause trouble for the circuit if we are not careful.
  • Notice what a difference the low distortion pinout makes in the layout of the board. The long feedback path is gone along its parasitic effects. Low distortion pinout enables compact and streamline layout
  • This board encompasses many if not all of the points made in this layout section. This board clearly illustrates the desired layout of keeping the bypass caps and the load resistors close and minimizes the interaction of other currents flowing in the ground plane. Multiple capacitors are used on the power supply pins to maintain a good low impedance across a wide frequency range. the small pads are used to minimize the effects of parasitics. This is a very desirable layout for high speed applications.
  • In the first module, we introduce the basic knowledge of high speed amplifiers. high speed amplifiers have bandwidth greater than 50MHz. They have two different topologies, voltage feedback and current feedback. Noise gain must be distinguished from signal gain. There are three amplifier architecture with different performance. using a resistor to isolate capacitive loading effects at an amplifier output is a good method to maintain performance and stability.
  • In the second module, the issues in PCB layout design have been discussed. Here highlight the key points in PCB layout design.
  • Here is more information for PCB design.
  • Thank you for taking the time to view this presentation on “ High Speed Amplifiers Part 3 ” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more technical information you may either visit the Analog Devices site – link shown – or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility.
  • High Speed Amplifiers Part 3

    1. 1. High Speed Amplifiers Part 3 <ul><li>Source: Analog Devices </li></ul>
    2. 2. Introduction <ul><li>Purpose </li></ul><ul><ul><li>This training module introduces the packing improvement for high speed amplifiers and summary the performance & design considerations of high speed amplifiers. </li></ul></ul><ul><li>Outline </li></ul><ul><ul><li>Packaging Innovation </li></ul></ul><ul><ul><li>High Speed Layout Techniques </li></ul></ul><ul><ul><li>Summary </li></ul></ul><ul><li>Content </li></ul><ul><ul><li>12 pages </li></ul></ul>
    3. 3. Op Amp Packaging and Pinout <ul><li>Packaging plays a large role in high-speed applications </li></ul><ul><li>Smaller packages </li></ul><ul><ul><li>Better at higher speeds </li></ul></ul><ul><ul><li>Compact layout </li></ul></ul><ul><li>Analog Devices Low Distortion Pinout </li></ul><ul><ul><li>Intuitively makes more sense </li></ul></ul><ul><ul><li>Compact layout </li></ul></ul><ul><ul><li>Streamline signal flow </li></ul></ul><ul><ul><li>Lower distortion </li></ul></ul>
    4. 4. Innovation Continues New Standard for High-Performance Op Amp Packaging <ul><li>Optimized for High-Speed </li></ul><ul><ul><li>Existing pin-out set 30+ years </li></ul></ul><ul><ul><ul><li>SO-8 will stay the same </li></ul></ul></ul><ul><ul><li>Take the lead in performance packages </li></ul></ul><ul><ul><li>New pin-out will maximize distortion and stability performance of AD8000, AD8099 and AD8045, ADA4899, ADA4857 </li></ul></ul><ul><ul><li>Customers benefit by easier layout </li></ul></ul><ul><li>LFCSP </li></ul><ul><ul><li>Better Thermals </li></ul></ul><ul><ul><li>Smaller Package 3mm X 3mm </li></ul></ul><ul><ul><li>Lower Parasitics Properties </li></ul></ul>Rotate Pin orientation by 1 Eliminates L coupling between –Vs / +IN A source of 2 nd harmonic distortion Isolating Feedback from Load Improves cap load stability Feedback N C 1 2 3 4 8 7 6 5   – IN – V S +IN +V S V OUT C C Disable + - Original Pin-Out
    5. 5. Distortion Comparison Standard Pin Out vs Low Distortion Pin Out 14dB
    6. 6. Op Amp SOIC Packaging <ul><li>Traditional SOIC-8 layout </li></ul><ul><li>Feedback routed around or underneath amplifier </li></ul>
    7. 7. Low Distortion Pinout
    8. 8. Low Distortion Pinout Tantalum Tantalum C C RL AD80XX RT RG RF 0 0
    9. 9. Summary 1 <ul><li>High Speed Amplifiers traditionally have BW >50Mhz </li></ul><ul><li>There are essentially two classes of op amps </li></ul><ul><ul><li>Voltage Feedback and Current Feedback </li></ul></ul><ul><ul><li>Voltage Feedback offer high input impedance, low noise and moderate slew rates </li></ul></ul><ul><ul><li>Current Feedback offers, Wide bandwidths at high and low gains, high slew rates.High impedance on the noninverting input, but have a low impedance on the inverting input, they can feature low voltage noise, but often have high current noise and bias currents. </li></ul></ul><ul><li>Signal Gain and Noise gain are two different parameters </li></ul><ul><li>Analog Devices AD8099, ADA4899 offers Wide Bandwidth, High Slew Rate and low noise in one op amp which features the Common Mode Linearized Input architecture. </li></ul><ul><li>Using a resistor to isolate capacitive loading effects at an amplifier output is a good method to maintain performance and stability. </li></ul>
    10. 10. Summary 2 <ul><li>High speed PCB design requires deliberate thought and attention to detail! </li></ul><ul><li>Load the schematic with as much information as possible </li></ul><ul><li>Where you put individual components on the board is just as important as to where you put entire circuits </li></ul><ul><li>Take the lead when laying out your board, don’t leave anything to chance </li></ul><ul><li>Use multiple capacitors for power supply bypassing </li></ul><ul><li>Parasitics must be considered and dealt with </li></ul><ul><li>Ground and Power planes play a key role in reducing noise and parasitics </li></ul><ul><li>New packaging and pinout options allow for improved performance and more compact layouts </li></ul><ul><li>There are many options for signal distribution, make sure you choose the right one for your application </li></ul><ul><li>Check the layout and check it again </li></ul><ul><li>Successful High Speed PCB design is a combination of education and experience and sometimes a little luck! </li></ul>
    11. 11. Summary 3 <ul><li>Work directly with PC board designer as they most likely will not understand proper RF layout techniques </li></ul><ul><li>Provide designer with a drawing of the location of the critical high frequency components and transmission lines </li></ul><ul><li>Instruct the board designer that transmission line widths and lengths are very critical and must be exactly as calculated </li></ul><ul><li>Place the components to minimize the length of RF interconnections </li></ul><ul><li>Generally try to place components in a “straight line” to avoid feedback loops and instabilities </li></ul><ul><li>Place circuit blocks such as oscillators, mixers, amplifiers in separate sections on the board if possible </li></ul><ul><li>Do NOT mix digital, low level analog, or bias traces with RF interconnects to avoid unwanted coupling </li></ul><ul><li>Locate the components operating at the highest frequencies close to board interconnects </li></ul><ul><li>With the PC board designer, check, and recheck the layout before sending out for fabrication </li></ul>
    12. 12. Additional Resource <ul><li>For ordering high speed operational amplifiers, please click the part list or </li></ul><ul><li>Call our sales hotline </li></ul><ul><li>For additional inquires contact our technical service hotline </li></ul><ul><li>For more product information go to </li></ul><ul><ul><li>http://www.analog.com/en/amplifiers-and-comparators/operational-amplifiers-op-amps/products/index.html </li></ul></ul>Newark Farnell