Datasheet LT1016 (Analog Devices) - 8

link to page 8 LT1016
APPLICATIONS INFORMATION
Other common problems include different measurement several devices connected to an unbypassed supply can results using various pieces of test equipment, inability “communicate” through the finite supply impedances, to make measurement connections to the circuit without causing erratic modes. Bypass capacitors furnish a simple inducing spurious responses and dissimilar operation way to eliminate this problem by providing a local reser- between two “identical” circuits. If the components used voir of energy at the device. The bypass capacitor acts in the circuit are good and the design is sound, all of the like an electrical flywheel to keep supply impedance low above problems can usually be traced to failure to pro- at high frequencies. The choice of what type of capaci- vide a proper circuit “environment.” To learn how to do tors to use for bypassing is a critical issue and should be this requires studying the causes of the aforementioned approached carefully. An unbypassed LT1016 is shown difficulties. responding to a pulse input in Figure 3. The power supply By far the most common error involves power supply the LT1016 sees at its terminals has high impedance at bypassing. Bypassing is necessary to maintain low sup- high frequency. This impedance forms a voltage divider ply impedance. DC resistance and inductance in supply with the LT1016, allowing the supply to move as internal wires and PC traces can quickly build up to unacceptable conditions in the comparator change. This causes local levels. This allows the supply line to move as internal feedback and oscillation occurs. Although the LT1016 current levels of the devices connected to it change. This responds to the input pulse, its output is a blur of 100MHz will almost always cause unruly operation. In addition, oscillation. Always use bypass capacitors.
TEST CIRCUIT
7404 TRACE A PULSE 5V/DIV GENERATOR 1k OUTPUTS 10Ω + TRACE B 5V/DIV LT1016 – TRACE C 5V/DIV VREF 10ns/DIV 1016 F02
Figure 2. LT1016 vs a TTL Gate
2V/DIV 100ns/DIV 1016 F03
Figure 3. Unbypassed LT1016 Response
Rev D 8 For more information www.analog.com Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Applications Information Typical Applications Appendix A Package Description Revision History Applications Information Related Parts