مدار مجتمع (آی سی) آی سی‌کاربرد ویژه

Product Attributes

Introduction

The AD891 Disk Channel Qualifier is designed as a companion chip to the AD890 Wideband Channel Processor. Together they form a sophisticated package capable of recovering binary information from a differential channel with data rates exceeding 50 megabits per second.

The AD891 provides both amplitude and time-domain qualification. Amplitude qualification is performed on alternate half-cycles of the data waveform using user-defined threshold levels applied to two comparators with 3.1 ns propagation delay. This technique prevents single-bit errors from propagating into two-bit errors. A third comparator is used to provide zero-crossing detection. Factory-trimmed offsets and careful internal layout ensure symmetrical operation and low pulse pairing for differential input waveforms.

An external RLC passive delay-line differentiator should be used with the AD891; the configuration of a typical network is detailed in the Applications section of the datasheet. The use of an external network ensures equal delay times in the differentiated and non-differentiated signal paths, thereby ensuring correct centering of the qualification window. Use of the recommended external network also helps ensure optimum signal passband flatness and dispersion.

The outputs from the amplitude qualification comparators are applied to the "D" inputs of two master-slave D-type flip-flops, which are then clocked by the output of the zero-crossing comparator. Each valid zero-crossing event triggers a monostable multivibrator with a user-definable period. This disables flip-flop operation, thereby preventing detection of additional zero-crossing events during the monostable period.

Simultaneously, an output monostable multivibrator is activated, with its leading edge synchronized to the transition of the flip-flop output. The period of this monostable multivibrator is also user-definable and is intended to ensure sufficient output pulse duration for propagation in the external environment. Each monostable multivibrator requires a metal film resistor to set its period. All monostable multivibrators feature trimmed pulse periods; temperature stability is maintained through the use of an internal bandgap reference.

The internal logic of the AD891 consists of temperature-compensated low-swing ECL with a typical propagation delay of 600 ps per gate. Output data conforms to standard 10KH ECL logic levels. The AD891 is capable of driving properly terminated 75 Ω transmission lines.

The AD891 operates over the commercial temperature range (0 to +70℃). It is available in a 14-pin ceramic DIP or a 20-pin plastic grid array package.

Applications

• Used with AD890 wideband channel processors to recover binary information at rates exceeding 50 Mbits/s from multiple channels.
• External RLC passive delay line differentiator ensures equal delay times for differentiated and non-differentiated signal paths, enabling proper alignment of the qualification window.
• Suitable for driving properly terminated 75Ω transmission lines.