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AD8152 Datasheet(PDF) 23 Page - Analog Devices |
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AD8152 Datasheet(HTML) 23 Page - Analog Devices |
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23 / 32 page  REV. A AD8152 –23– ECL DRIVER TO 50 SCOPE INPUTS VCC VTTO VTTI = –2V VEE = –2.5V AD8152 PP NN IN OUT Figure 15. Evaluation Board ECL Driver Test Setup Connections for Testing The AD8152 evaluation board can be used under a variety of posi- tive or negative supply configurations. Negative supply configurations, as shown in Figure 15, allow the easiest hookup to test equip- ment because inputs and outputs can be direct coupled. In a real world application however, the negative supply configuration would be difficult because control logic levels must be shifted negative. Figure 16 is an example of a loop-through test setup using a posi- tive supply. In this case, the test signal goes through the AD8152 twice. It is possible to loop through multiple times if desired, but jitter will increase with number of loop-throughs. The first input from the generator and the last output to a scope must be ac-coupled. However, an AD8152 output driving its own input can be direct-coupled. Direct coupling to the first AD8152 input is not effective since generators usually want to see 50 W to ground. This would require VTTI to be attached to ground, causing excessive power to be dissipated in the internal 50 W input termination resistors. Secondly, when the AD8152 output tries to drive its own input with VTTI = 0 V and VTTO = 2.5 V, the input will pull the output stage levels down enough to shut off any signal toggling. All ac coupling shown is actually done with a set of bias tees. If desired, the bias tee can be used to monitor average dc voltage levels at an input or output (depending on direction installed), and it can also serve to change input dc levels. Make sure the bias tees used in the setup have enough low frequency bandwidth to pass long patterns and keep edge rates intact. The longer the pattern, the more low frequency bandwidth is needed. If ac coupling is desired on a user board, 0402 or 0603 sized capacitors can be installed on microstrip lines. The biggest 0402 size, XR7 type usable is 0.01 mF, which will work fine for short patterns (PRBS 2 7–1) and data rates down to 1.0 Gbps. For long patterns a 0603 sized, XR7 type, 0.1 mF should be used. To decrease capacitive loading from the mounting area, clear out planes underneath the coupling capacitor. In Figure 16, 6 dB attenuators are placed before the AD8152 input ac-coupling or bias tees. This is because many generators won’t go below 500 mV single-ended. The output pair of 6 dB attenuators is present to protect the scope inputs and allow for higher scale voltages per division. The eye diagram is usually viewed differentially by using a simple P – N math function. Cabling used in this setup must be matched. Mismatched cables cause either a P or N signal to be falsely delayed. This delay can show up as a change in the crossing point, from 50 percent in the eye diagram. To accurately check cable matches, a TDR setup is recommended. PATTERN GENERATOR VCC VTTO 2.5V AD8152 P P N N IN01 OUT01 VTTI P N P N IN02 OUT02 VEE 50 50 DATA OUT DATA OUT TRIGGER OUT TRIGGER IN HIGH SPEED SAMPLING OSCILLOSCOPE –6dB –6dB –6dB –6dB VCC = VTTI = VTTO = 2.5V, VEE = 0V,I OUT SET = 16mA RTI (REFERRED TO INPUT)A MPLITUDE = 400mV SINGLE–ENDED, VIN HI = 2.7V (IN01), PRBS 223 –1, VOH = 2.5V, VOL = 2.1V, AC-COUPLED IS FROM BIAS TEES, PROGRAMMING: IN01 TO OUT02, IN02 TO OUT01. Figure 16. Positive Supply Loop-Through Test Setup |
Similar Part No. - AD8152_15 |
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Similar Description - AD8152_15 |
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