Lattice GAL20V8B-15LPI: Architecture, Key Features, and Application Design Considerations
The Lattice GAL20V8B-15LJPI stands as a quintessential example of a high-performance, low-power programmable logic device (PLD) from the Generic Array Logic (GAL) family. As a CMOS-based device, it offers a robust and flexible solution for integrating complex combinatorial and sequential logic, serving as a hardware-efficient alternative to discrete logic gates. Its 15ns maximum propagation delay (tPD) makes it suitable for a wide range of high-speed applications.
Architecture Overview
The architecture of the GAL20V8B is centered around a programmable AND array feeding into a fixed OR array. This structure effectively implements sum-of-products logic functions. The key architectural components include:
Input/Output Logic Macrocells (OLMCs): The device features 8 output logic macrocells, each of which can be individually configured for combinatorial or registered operation. This is the core of its flexibility, allowing each pin to be defined as an input, an output, or a bidirectional pin.
Programmable AND Array: This array consists of programmable links that define the logic functions. The "20" in its name refers to the inputs to this array, while the "8" denotes the number of outputs.
Output Register: Each macrocell contains a D-type flip-flop that can be used for registered outputs, enabling the design of state machines and counters.
Key Features
The GAL20V8B-15LJPI is characterized by several critical features that have cemented its longevity in the electronics industry:
High Speed: The `-15` suffix indicates a maximum propagation delay of 15 nanoseconds, ensuring rapid response times for critical logic paths.
Low Power Consumption: Fabricated in advanced CMOS technology, it consumes significantly less power than its bipolar (e.g., PAL) predecessors, making it ideal for power-sensitive designs.
Electrically Erasable (E²) Technology: The use of E²CMOS cells makes the device reprogrammable and highly reusable. Design iterations can be made quickly without removing the chip from the circuit board, vastly accelerating development and debugging.
100% Testability: The architecture supports functional testability, ensuring that the programmed device can be verified against its intended logic design.
Security Fuse: A built-in programmable security bit prevents unauthorized copying or reverse-engineering of the programmed logic pattern, protecting intellectual property.
Application Design Considerations
When designing with the GAL20V8B, several factors must be carefully considered to ensure optimal performance and reliability:
1. Power-On Reset (POR): The internal registers require a stable power-on reset sequence. Designers must ensure the supply voltage ramps up cleanly and quickly to initialize the device to a known state, preventing erratic startup behavior.
2. Clock and Input Signal Integrity: Given its high-speed capability, signal integrity is paramount. Clock signals must be clean and free from ringing or overshoot. Input signals must meet the specified setup and hold times (tSU and tH) relative to the clock edge for registered configurations.
3. Output Loading: The device's outputs have limited drive capability. Designers must calculate the total capacitive load on each output pin to avoid exceeding maximum current ratings and to prevent signal degradation that could increase propagation delays.
4. Thermal Management: While power consumption is low, the total power dissipation (sum of internal and I/O power) must be calculated to ensure the device operates within its specified junction temperature range, especially in high-temperature environments.
5. Programming and Verification: Utilizing a reliable, certified programmer is essential. Always verify the programmed pattern against the original JEDEC file to catch any programming errors. Furthermore, it is good practice to perform a functional test under real-world operating conditions.
The Lattice GAL20V8B-15LJPI remains a versatile and reliable workhorse in digital logic design. Its blend of high speed, low power, and in-circuit reconfigurability provides an excellent solution for glue logic, state machine control, and address decoding. For engineers, understanding its architecture and adhering to key design considerations are fundamental to leveraging its full potential and ensuring robust system integration.
Keywords: Programmable Logic Device (PLD), E²CMOS Technology, Output Logic Macrocell (OLMC), Propagation Delay, JEDEC File.
