Datasheet MAX9691, MAX9692, MAX9693 (Maxim) - 6

Single/Dual, Ultra-Fast, ECL-Output Comparators with Latch Enable __________ Applications Information
problems when the input goes through the linear region. For clean switching without oscillation or steps
Layout
in the output waveform, the input must meet certain Because of the MAX9691/MAX9692/MAX9693s’ large minimum slew-rate requirements. The tendency of the gain-bandwidth characteristic, special precautions part to oscillate is a function of the layout and source must be taken to use them. A PC board with a ground impedance of the circuit employed. Poor layout and plane is mandatory. Mount 0.01µF ceramic decoupling larger source impedance will increase the minimum capacitors as close to the power-supply pins as possi- slew-rate requirement. ble, and process the ECL outputs in microstrip fashion, Figure 1 shows a high-speed receiver application with consistent with the load termination of 50Ω to 200Ω (for 50Ω input and output termination. With this configura- VT = -2V). For low-impedance applications, microstrip tion, in which a ground plane and microstrip PC board layout and terminations at the input may also be help- are used, the minimum slew rate for clean output ful. Pay close attention to the bandwidth of the decou- switching is 1V/µs. pling and terminating components. Chip components can be used to minimize lead inductance. Connect In many applications, adding regenerative feedback GND1 and GND2 together to a solid copper ground will assist the input signal through the linear region, plane for the MAX9691/MAX9692. GND1 biases the which will lower the minimum slew-rate requirement input gain stages, while GND2 biases the ECL output considerably. For example, with the addition of positive stage. If the LE function is not used, connect the LE pin feedback components, Rf = 1kΩ and Cf = 10pF, the to GND (MAX9692/MAX9693) and the complementary minimum slew-rate requirement can be reduced by a LE to ECL logic high level (MAX9693 only). Do not factor of four. leave the inputs of an unused comparator floating for As high-speed receivers, the MAX9691/MAX9692/ the MAX9693. MAX9693 are capable of processing signals in excess of 600MHz. Figure 2 is a 100MHz example with an
Input Slew-Rate Requirements
input signal level of 14mVRMS. As with all high-speed comparators, the high gain- bandwidth product of these devices creates oscillation
MAX9691/MAX9692/MAX9693
VIN Q 50Ω Q INPUT LE 0V 50Ω 20mV/div -2V OUTPUT -0.9V R 500mV/div f Cf 50Ω 50Ω -1.7V 2ns/div Figure 1. Regenerative Feedback—High-Speed Receiver with Figure 2. Signal Processed at 100MHz with Input Signal Level 50Ω Input and Output Termination of 14mVRMS
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