AD8561AR

The AD8561AR is a high-speed single-supply comparator from Analog Devices, delivering 7 ns propagation delay at 5V while consuming very low supply current. This single comparator features separate input and output power supply sections, enabling the input stage to operate from plus/minus 5V dual supplies or a single +5V supply independently from the output supply, providing flexibility for interfacing with different logic families. The PNP differential input stage offers a wide common-mode input range that extends all the way from the negative supply rail to within 2.2V of the positive supply, allowing the device to handle ground-referenced signals in single-supply applications. A key advantage of the AD8561AR is its closely matched propagation delays for rising and falling edges, which remain well matched across temperature variations. This characteristic ensures that the output duty cycle accurately tracks the input duty cycle, making the device particularly well-suited for clock recovery circuits where duty cycle distortion must be minimized. The integrated latch function adds another dimension of versatility, allowing the comparator output to be sampled and held under external control. The AD8561AR is pin-compatible with the industry-standard LT1016 comparator but offers improved performance including lower supply current and a wider common-mode input range. The device is available in 8-lead SOIC (small-outline integrated circuit) package, as well as PDIP and TSSOP options, and is specified for operation over the full industrial temperature range of -40 degrees C to +85 degrees C. For optimal high-speed performance, careful PCB layout practices including ground planes, proper bypass capacitance, and minimizing source impedance are recommended. The AD8561AR is supported by LTspice simulation models and extensive application documentation from Analog Devices.

The AD8561AR is a high-speed voltage comparator that operates by comparing two analog input voltages and producing a digital output indicating which input is larger. The input stage consists of a PNP differential pair that converts the voltage difference between the two inputs into a current difference. This current difference is then amplified by subsequent gain stages and drives an output stage that provides a digital logic level output. The PNP input topology is what gives the AD8561AR its wide common-mode range extending to the negative supply rail, since PNP transistors can operate with their emitters at or near the negative supply voltage. The input bias current of approximately 3 microamps flows out of the inputs (a characteristic of PNP stages), and this current must be considered when choosing source resistance values. The comparator features separate VCC supply pins for the input section and the output section, allowing the output to be powered from a different voltage than the input stage. This enables direct interfacing with different logic families – for example, the input can run from plus/minus 5V while the output runs from a single 5V supply for TTL/CMOS compatibility. The latch function operates by adding a flip-flop stage at the output. When the latch enable is active, the output follows the input comparison result (transparent mode). When the latch is triggered (hold mode), the output state at that moment is captured and held regardless of subsequent input changes. This is useful for sampling applications where the comparison result must be stable during a read operation. The propagation delay of 7 ns represents the time between a step change at the input and the corresponding transition at the output. For best performance, a sufficiently large overdrive voltage (typically 100 mV or more) should be applied, as smaller overdrive voltages result in longer propagation delays.

• Clock recovery circuits in high-speed data communication systems
• High-speed timing and pulse-width measurement circuits
• Line receivers and signal threshold detection
• Phase detector and frequency discriminator circuits
• Zero-crossing detectors for AC signal monitoring
• Window comparators for voltage window monitoring
• Sampled data systems and analog-to-digital converter frontends
• PCMCIA cards and portable test equipment
• Read channel detection in disk drive and data storage systems
• Level translation between different voltage domains