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74ACTQ18823MTD Datasheet(PDF) 7 Page - Fairchild Semiconductor |
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74ACTQ18823MTD Datasheet(HTML) 7 Page - Fairchild Semiconductor |
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7 / 9 page  7 www.fairchildsemi.com FACT Noise Characteristics The setup of a noise characteristics measurement is critical to the accuracy and repeatability of the tests. The following is a brief description of the setup used to measure the noise characteristics of FACT. Equipment: Hewlett Packard Model 8180A Word Generator PC-163A Test Fixture Tektronics Model 7854 Oscilloscope Procedure: 1. Verify Test Fixture Loading: Standard Load 50 pF, 500 Ω. 2. Deskew the HFS generator so that no two channels have greater than 150 ps skew between them. This requires that the oscilloscope be deskewed first. It is important to deskew the HFS generator channels before testing. This will ensure that the outputs switch simultaneously. 3. Terminate all inputs and outputs to ensure proper load- ing of the outputs and that the input levels are at the correct voltage. 4. Set the HFS generator to toggle all but one output at a frequency of 1 MHz. Greater frequencies will increase DUT heating and affect the results of the measure- ment. VOHV and VOLP are measured with respect to ground reference. Input pulses have the following characteristics: f = 1MHz, t r = 3ns, tf = 3 ns, skew < 150 ps. FIGURE 1. Quiet Output Noise Voltage Waveforms 5. Set the HFS generator input levels at 0V LOW and 3V HIGH for ACT devices and 0V LOW and 5V HIGH for AC devices. Verify levels with an oscilloscope. VOLP/VOLV and VOHP/VOHV: • Determine the quiet output pin that demonstrates the greatest noise levels. The worst case pin will usually be the furthest from the ground pin. Monitor the output volt- ages using a 50 Ω coaxial cable plugged into a standard SMB type connector on the test fixture. Do not use an active FET probe. • Measure VOLP and VOLV on the quiet output during the worst case transition for active and enable. Measure VOHP and VOHV on the quiet output during the worst case active and enable transition. • Verify that the GND reference recorded on the oscillo- scope has not drifted to ensure the accuracy and repeat- ability of the measurements. VILD and VIHD: • Monitor one of the switching outputs using a 50 Ω coaxial cable plugged into a standard SMB type connector on the test fixture. Do not use an active FET probe. • First increase the input LOW voltage level, VIL, until the output begins to oscillate or steps out a min of 2 ns. Oscillation is defined as noise on the output LOW level that exceeds VIL limits, or on output HIGH levels that exceed VIH limits. The input LOW voltage level at which oscillation occurs is defined as VILD. • Next decrease the input HIGH voltage level, VIH, until the output begins to oscillator steps out a min of 2 ns. Oscillation is defined as noise on the output LOW level that exceeds VIL limits, or on output HIGH levels that exceed VIH limits. The input HIGH voltage level at which oscillation occurs is defined as VIHD. • Verify that the GND reference recorded on the oscillo- scope has not drifted to ensure the accuracy and repeat- ability of the measurements. FIGURE 2. Simultaneous Switching Test Circuit |
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