Lattice GAL20V8B-7LP: Architecture, Features, and Application Design Considerations

The Lattice GAL20V8B-7LP stands as a quintessential example of a high-performance, low-power programmable logic device (PLD) from the Generic Array Logic (GAL) family. As a 7.5ns maximum propagation delay device, it is engineered for applications requiring both speed and power efficiency. Understanding its architecture, core features, and key design considerations is crucial for effective implementation in modern digital systems.

Architecture and Core Functional Blocks

The GAL20V8B-7LP is built around a well-established, yet powerful, architecture centered on a programmable AND array and a fixed OR array. This structure efficiently implements sum-of-product logic functions. The "20" in its designation refers to the number of inputs, while the "V8" indicates that up to eight outputs can be configured, each through an Output Logic Macrocell (OLMC).

Each OLMC is the heart of the device's flexibility. It can be individually configured by the user to operate in various modes:

Combinatorial Mode: The output is a direct function of the input signals from the AND array.

Registered Mode: The output is stored in a D-type flip-flop, synchronized to a clock signal, enabling the design of sequential logic circuits like counters and state machines.

Complex Mode: Allows for more sophisticated input/output configurations, making some pins bidirectional.

This programmability is achieved through electrically erasable (E²) CMOS technology, which allows the device to be reprogrammed multiple times, facilitating rapid design iteration and prototyping.

Key Features and Advantages

The GAL20V8B-7LP is characterized by several defining features that make it a compelling choice for many designs:

High Speed: With a maximum propagation delay (tPD) of 7.5ns, it is suitable for high-speed logic integration, replacing multiple standard logic ICs and reducing board space.

Low Power Consumption: Fabricated in advanced CMOS technology, it features significantly lower power consumption than its bipolar (e.g., PAL) predecessors, making it ideal for portable and battery-operated equipment.

100% Testability: The logic functionality is 100% testable via a proprietary test circuitry, ensuring high production yields and system reliability.

E²CMOS Technology: This technology provides reprogrammability and non-volatile configuration storage. The device retains its programmed pattern even when power is removed, eliminating the need for external configuration memory.

Electrostatic Discharge (ESD) Protection: Robust ESD protection on all pins enhances the device's durability and handling safety during production.

Critical Application Design Considerations

Successfully integrating the GAL20V8B-7LP into a system requires careful attention to several design aspects:

1. Power-On Reset (POR) Behavior: The internal registers have a defined power-on reset state, which is critical for ensuring the system starts in a known and stable condition. Designers must verify that this default state aligns with their system's requirements.

2. Clock and Signal Integrity: In registered mode, the setup and hold times for data relative to the clock signal must be strictly adhered to. Proper clock distribution and signal integrity practices are essential to prevent metastability and ensure reliable operation at high speeds.

3. Output Loading and Fanout: While the outputs can source or sink significant current, excessive capacitive loading can degrade signal edges and increase propagation delays. Calculating the total fanout and capacitive load is necessary to maintain signal integrity.

4. Thermal Management: Although a low-power device, the total power dissipation (calculated as Icc Vcc plus the cumulative power of switching outputs) should be evaluated to ensure the package operates within its safe temperature range.

5. Programming and Security: Utilizing a high-quality programmer supported by the chosen design software (e.g., CUPL, Abel) is vital. The device also offers a security fuse that, once programmed, prevents the pattern from being read back, protecting intellectual property.

ICGOOODFIND

The Lattice GAL20V8B-7LP remains a highly effective solution for consolidating glue logic, implementing state machines, and performing high-speed interface translation. Its blend of speed, low power, and design flexibility offers a reliable and cost-effective means to simplify circuit design, enhance reliability, and reduce the overall component count in a wide array of electronic systems.

Keywords: Programmable Logic Device (PLD), Output Logic Macrocell (OLMC), Low Power Consumption, Reprogrammable, Propagation Delay.