AD9026 12-BIT. 31MSPS ADC EVALUATION BOARD ANALOG Figure 9.16 The output connector is designed for convenient interfacing to an external buffer The top side of the board is shown in Figure 9. 17. The board is a 3-layer board ory) memory or to a logic analyzer input (a very convenient high speed buffer memo consisting of one ground plane(outer layer), one power/signal plane (inner layer) and an additional signal plane(outer layer). Pin sockets are used to mount the AD9026. Figure 9 18 shows the bottom side of the board and the surface mounted AD9698 SOIC comparator and the aD9713B PLCC dac AD9026 EVALUATION BOARD- TOP VIEW RC OUTPUT ANALO 圆 AD9026 EVALUATION BOARD Figure 9.17
1 6 AD9026 12-BIT, 31MSPS ADC EVALUATION BOARD Figure 9.16 The output connector is designed for convenient interfacing to an external buffer memory or to a logic analyzer input (a very convenient high speed buffer memory). The top side of the board is shown in Figure 9.17. The board is a 3-layer board consisting of one ground plane (outer layer), one power/signal plane (inner layer), and an additional signal plane (outer layer). Pin sockets are used to mount the AD9026. Figure 9.18 shows the bottom side of the board and the surface mounted AD9698 SOIC comparator and the AD9713B PLCC DAC. AD9026 EVALUATION BOARD - TOP VIEW Figure 9.17
AD9026 EVALUATION BOARD- BOTTOM VIEW 四图 Figure 9. 18
1 7 AD9026 EVALUATION BOARD - BOTTOM VIEW Figure 9.18
REFERENCES: PROTOTYPING AND EVALUATION BOARDS 1. Robert A Pease, Troubleshooting Analog Circuits, Butterworth nn,1991 2. Wainwright Instruments Inc, 7770 Regents Rd, #113, Suite 371 San diego,CA92122,Tel.619-558-1057,Fax.619-558-1019 Wainwright Instruments Gmbh, widdersberger Strasse 14 DW-8138 Andechs-Frieding, Germany. Tel: +49-8152-3162 Fax:+49815240525 3 Schematic Capture and Layout Software PADS Software, INC, 165 Forest St, Marlboro, MA, 01752 ACCEL Technologies, Inc, 6825 Flanders Dr, San Diego, CA, 92121 4. Prototype Board Cutters LPKF CAD/CAM SyStems. Inc.. 1800 NW 169th Place Beaverton. OR. 97006 T-Tech, Inc, 5591-B New Peachtree Road, Atlanta, GA, 34341
1 8 REFERENCES: PROTOTYPING AND EVALUATION BOARDS 1. Robert A. Pease, Troubleshooting Analog Circuits, ButterworthHeinemann, 1991. 2. Wainwright Instruments Inc., 7770 Regents Rd., #113, Suite 371, San Diego, CA 92122, Tel. 619-558-1057, Fax. 619-558-1019. Wainwright Instruments GmbH, Widdersberger Strasse 14, DW-8138 Andechs-Frieding, Germany. Tel: +49-8152-3162, Fax: +49-8152-40525. 3. Schematic Capture and Layout Software: PADS Software, INC, 165 Forest St., Marlboro, MA, 01752 ACCEL Technologies, Inc., 6825 Flanders Dr., San Diego, CA, 92121 4. Prototype Board Cutters: LPKF CAD/CAM Systems, Inc., 1800 NW 169th Place, Beaverton, OR, 97006 T-Tech, Inc., 5591-B New Peachtree Road, Atlanta, GA, 34341
NOISE REDUCTION AND FILTERING FOR SWITCHING POWER SUPPLIES Walt Jung and John McDonald Precision analog circuitry has traditionally been powered from well regulated, low noise linear power supplies. During the last decade however, switching power supplies have become much more common in electronic systems. As a consequence popularity,including high efficiency, low temperature rise, small size, and ligh their they also are being used for analog supplies There are several good reasons for weight Switching power supplies, or more simply switchers, a category including switching regulators and switching converters, are by their nature efficient. Often this can be above 90%, and as a result, these power supply types use less power and generate less heat than do equivalent linear supplies A switcher can be as much as one third the size and weight of a linear supply delivering the same voltage and current Switching frequencies can range from 20kHz to 1MHz, and as a result, relatively small components can be used in their de In spite of these benefits, switchers have their drawbacks, most notably high output noise. This noise generally extends over a broad band of frequencies, and occurs as both conducted and radiated noise and unwanted electric and magnetic fields Voltage output noise of switching supplies are short-duration voltage transients, or spikes. Although the fundamental switching frequency can range from 20kHz to 1MHz, the voltage spikes will contain frequency components extending easily to 100MHz or more Because of wide variation in the noise output characteristics of commercial switchers, they should always be purchased in accordance with a specification control drawing. Although specifying switching supplies in terms of RMs noise is common vendor practice, as a user you should also specify the peak(or p-p amplitudes of the switching spikes, with the output loading of your system. You should also insist that the switching supply manufacturer inform you of any internal supply design changes that may alter the spike amplitudes, duration, or switching frequency. These changes may require corresponding changes in external filtering
1 9 NOISE REDUCTION AND FILTERING FOR SWITCHING POWER SUPPLIES Walt Jung and John McDonald Precision analog circuitry has traditionally been powered from well regulated, low noise linear power supplies. During the last decade however, switching power supplies have become much more common in electronic systems. As a consequence, they also are being used for analog supplies. There are several good reasons for their popularity, including high efficiency, low temperature rise, small size, and light weight. Switching power supplies, or more simply switchers, a category including switching regulators and switching converters, are by their nature efficient. Often this can be above 90%, and as a result, these power supply types use less power and generate less heat than do equivalent linear supplies. A switcher can be as much as one third the size and weight of a linear supply delivering the same voltage and current. Switching frequencies can range from 20kHz to 1MHz, and as a result, relatively small components can be used in their design. In spite of these benefits, switchers have their drawbacks, most notably high output noise. This noise generally extends over a broad band of frequencies, and occurs as both conducted and radiated noise, and unwanted electric and magnetic fields. Voltage output noise of switching supplies are short-duration voltage transients, or spikes. Although the fundamental switching frequency can range from 20kHz to 1MHz, the voltage spikes will contain frequency components extending easily to 100MHz or more. Because of wide variation in the noise output characteristics of commercial switchers, they should always be purchased in accordance with a specificationcontrol drawing. Although specifying switching supplies in terms of RMS noise is common vendor practice, as a user you should also specify the peak (or p-p) amplitudes of the switching spikes, with the output loading of your system. You should also insist that the switching-supply manufacturer inform you of any internal supply design changes that may alter the spike amplitudes, duration, or switching frequency. These changes may require corresponding changes in external filtering networks
SWITCHING POWER SUPPLY CHARACTERISTICS ADVANTAGES Efficient Small Size, Light Weight Low Operating Temperature Rise Isolation from Line transients Wide Input/Output Range DISADVANTAGES: Noise: LF, HF, Electric Field, Magnetic Field Conducted, Radiated dc requlation and accuracy can be poor Figure 9.19 This section discusses filter techniques for rendering a noisy switcher output analo ready, that is sufficiently quiet to power precision analog circuitry with relatively small loss of dC terminal voltage. These techniques include characterization of switcher output noise, identification of the frequency range of interference produced by the switching power supply, evaluation of passive components commonly used in external power supply filters, and the design and construction of a switching power supply filter. The filter solutions presented are generally applicable to all power supply types incorporating a switch element in their energy path This includes various DC-DC converters, as well as the 5v PC type supply used in the example A TYPICAL 5V,150W PC SWITCHING POWER SUPPLY Figure 9.20
2 0 SWITCHING POWER SUPPLY CHARACTERISTICS ADVANTAGES: Efficient Small Size, Light Weight Low Operating Temperature Rise Isolation from Line Transients Wide Input/Output Range DISADVANTAGES: Noise: LF, HF, Electric Field, Magnetic Field Conducted, Radiated DC regulation and accuracy can be poor Figure 9.19 This section discusses filter techniques for rendering a noisy switcher output analog ready, that is sufficiently quiet to power precision analog circuitry with relatively small loss of DC terminal voltage. These techniques include characterization of switcher output noise, identification of the frequency range of interference produced by the switching power supply, evaluation of passive components commonly used in external power supply filters, and the design and construction of a switching power supply filter. The filter solutions presented are generally applicable to all power supply types incorporating a switch element in their energy path. This includes various DC-DC converters, as well as the 5V PC type supply used in the example. A TYPICAL 5V, 150W PC SWITCHING POWER SUPPLY Figure 9.20