In the realm of precision motion control, the accurate measurement of angular position and velocity is paramount. Resolvers, being rugged and reliable sensors capable of operating in harsh environments, are often the transducer of choice. Bridging the analog world of the resolver to the digital domain of modern processors requires a specialized component: the resolver-to-digital converter (RDC). The **AD2S99AP from Analog Devices** stands as a quintessential interface solution, designed specifically to provide the excitation signal required for these critical sensors. This article delves into the technical intricacies and practical applications of this key component.
**Technical Architecture and Core Functionality**
The AD2S99AP is not a complete RDC itself but an **essential companion IC** to tracking converters like the industry-standard AD2S90 or AD2S1200. Its primary function is to generate the high-frequency, low-distortion sinusoidal reference signal needed to excite the primary winding of a resolver. The device operates from a single +5V supply and typically generates a **4 Vp-p, 10 kHz sine wave**, a common standard for many resolver systems.
Internally, the AD2S99AP employs a sophisticated **phase-locked loop (PLL)** architecture. This design ensures that its output excitation frequency is precisely synchronized to an external clock input provided by the companion RDC. This synchronization is critical as it eliminates any phase error that could be introduced between the excitation and the demodulation process happening inside the RDC, thereby guaranteeing maximum accuracy in the position reading.
Key performance features include:
* **Low Harmonic Distortion:** The on-chip sine wave synthesizer produces a clean output signal, which is crucial for minimizing errors in the resolver's output signals.
* **Programmable Frequency:** While often used at 10 kHz, the output frequency is set by the external clock, offering flexibility for different system requirements.
* **High Output Drive:** It can directly drive the low impedance of a resolver's primary winding, typically **30 Ω minimum**, eliminating the need for an external buffer amplifier.
**Application Circuit Design and Implementation**
Integrating the AD2S99AP into a system is straightforward. The typical application circuit involves connecting a external clock signal from the master RDC to the AD2S99AP's CLKIN pin. The device then generates the sine wave output (SINEOUT) and a complementary signal (COSINEOUT) which can be used for diagnostic purposes.
A critical part of the external circuit design is the **output filtering**. The square wave generated internally is filtered through a simple external LC filter to form the final sinusoidal waveform. The values of the inductor (L) and capacitor (C) are selected based on the desired excitation frequency to effectively attenuate any higher-order harmonics. Proper PCB layout is also essential, with attention to grounding and decoupling, to maintain signal integrity and prevent noise from degrading system performance.
**Addressing Key Design Challenges**
The AD2S99AP effectively solves several common design challenges:
1. **System Synchronization:** Its PLL-based design ensures the excitation signal is perfectly locked to the system clock, a task that would be complex and component-heavy with discrete oscillators.
2. **Component Count Reduction:** By integrating the oscillator, PLL, and output drivers into a single 16-pin DIP or SOIC package, it significantly reduces board space and design complexity compared to discrete solutions.
3. **Improved Reliability:** The monolithic construction offers higher reliability and temperature stability than a design built from separate op-amps, oscillators, and filters.
**Typical Use Cases**
The AD2S99AP finds its home in a vast array of high-performance industrial, automotive, and aerospace systems, including:
* **Servo motor control** systems for robotics and CNC machinery.
* **Electric power steering (EPS)** systems in vehicles.
* **Avionics** such as flight surface actuators and cockpit instrument control.
* **Precision test and measurement** equipment.
ICGOODFIND: The **AD2S99AP** is a highly specialized and optimized solution that serves a single purpose exceptionally well. It remains a fundamental building block for creating robust, accurate, and reliable resolver-based motion feedback systems, effectively offloading a critical task from the digital converter and ensuring optimal system-level performance.
**Keywords:** Resolver-to-Digital Converter, Excitation Signal, Phase-Locked Loop (PLL), Harmonic Distortion, Motion Control.
