AD633: Datasheet, Pinout, and Modulation Guide

Executive Summary: What is the AD633?

The AD633 is a low-cost, functionally complete, four-quadrant analog multiplier designed for real-time operations such as modulation, demodulation, and power measurement without the need for complex external components. 

Market Position: An industry-standard, low-cost solution for analog signal processing, balancing price with laser-trimmed accuracy.

Top Features: High impedance differential X and Y inputs (10 MΩ), 10 V full-scale output, and complete monolithic integration (no external trimming required).

• Primary Audience: Ideal for analog design engineers, audio synthesizer developers (Eurorack), and students working on instrumentation projects.

• Supply Status: Active and In Stock. (Refer to distributor listings for real-time quantities).

AD633 product photo

1. Technical Specifications & Performance Analysis

1.1 Core Architecture (Functionality)

The AD633 operates as a translinear analog multiplier. Unlike earlier generations that required extensive external circuitry, it includes a buried Zener reference and a unity gain summing amplifier. It performs the transfer function $W = \frac{(X1-X2)(Y1-Y2)}{10V} + Z$, making it incredibly versatile for algebraic analog operations. The "Brain" of this chip is its ability to handle four-quadrant multiplication, meaning it accepts positive and negative voltages on both inputs.

1.2 Key Electrical Characteristics

Engineers must verify these operating limits to ensure design stability:

• Supply Voltage: ±8 V to ±18 V (Dual supply required).

• Bandwidth: 1 MHz (-3 dB small signal).

• Slew Rate: 20 V/µs typical.

• Total Error: Within 2% of full scale (Laser-trimmed).

• Input Impedance: 10 MΩ on X and Y inputs, minimizing loading effects on source signals.

1.3 Interfaces and Connectivity

The AD633 is a purely analog device. It does not use digital buses like I2C or SPI. - Inputs: Differential high-impedance inputs (X1, X2, Y1, Y2) allow for easy interfacing with op-amps and sensors. - Summing Input: The Z input allows the cascading of multipliers or the addition of signals for mixing applications. - Output: Low impedance output (W) drives loads directly (nominal 10 V full scale).

AD633 functional block diagram

2. Pinout, Package, and Configuration

2.1 Pin Configuration Guide

The AD633 typically comes in an 8-lead package. Understanding the differential inputs is key to avoiding ground loops.

AD633 pinout diagram

• Pin 1 & 2 (X1, X2): Differential X inputs. 

• Pin 3 & 4 (Y1, Y2): Differential Y inputs. 

• Pin 5 (V-): Negative Power Supply (e.g., -15V).

• Pin 6 (Z): Summing Input.

• Pin 7 (W): Product Output.

• Pin 8 (V+): Positive Power Supply (e.g., +15V).

2.2 Naming Convention & Ordering Codes

Understanding the Part Numbers:

• Suffix "A" vs "J": Denotes accuracy grade and temperature range. 

• Suffix "N": PDIP Package (Plastic Dual In-Line Package).

• Suffix "R" or "RZ": SOIC Package (Small Outline typical for SMD). "Z" indicates RoHS/Lead-Free.

• Suffix "EP": Enhanced Product (Aerospace/Defense grade).

2.3 Available Packages

3. Design & Integration Guide (For Engineers & Makers)

Pro Tip: While the AD633 is robust, it is sensitive to power supply noise. Always verify pin compatibility if migrating from the AD534, as pinouts differ.

3.1 Hardware Implementation

• Bypass Capacitors: Place 0.1 µF ceramic capacitors in parallel with 10 µF electrolytic capacitors as close as possible to Pin 5 (V-) and Pin 8 (V+) to filter supply ripple.

• PCB Layout: Use a solid ground plane. Keep the input traces (X/Y) away from high-current switching traces to prevent capacitive coupling.

• Thermal Management: The standard SOIC/PDIP packages generally operate without heatsinks under normal load conditions given the low quiescent current.

3.2 Common Design Challenges

Below are common issues reported by designers, with solutions derived from technical forums and datasheets.

1. Issue: Noise Floor in Audio Applications

• Symptom: Audible hiss in synthesizer VCA designs.

• Fix: The AD633 is general-purpose. For high-fidelity audio, consider a dedicated VCA like the THAT2181 or implement aggressive low-pass filtering on the output.

2. Issue: Bandwidth Limitations (RF)

• Symptom: Signal roll-off when working with frequencies >1 MHz.

• Fix: The 1 MHz bandwidth is insufficient for RF. Switch to high-speed multipliers like the AD835 for MHz-range signals.

3. Issue: Feedthrough Leakage

• Symptom: Signal leaks from Input X to Output W even when Input Y is zero.

• Fix: Utilize the Z-input for offset nulling to cancel out feedthrough or select higher-grade variants.

4. Typical Applications & Use Cases

The AD633 is extensively used in:

• Analog Computing: Real-time squaring and division.

• Modulation: Amplitude Modulation (AM) and Ring Modulation.

• Power Measurement: Instantaneous power calculation ($P = V \times I$).

4.1 Real-World Example: Voltage-Controlled Amplifier (VCA)

In analog synthesizers, the AD633 acts as a VCA. An audio signal is applied to the X input, and a control voltage (Envelope Generator) is applied to the Y input. The multiplier scales the audio amplitude based on the control voltage, effectively controlling the "volume" dynamically to create the note's envelope (Attack, Decay, Sustain, Release).

5. Alternatives and Cross-Reference Guide

• Direct Replacements & Competitors:

• Texas Instruments MPY634: Extremely popular alternative, often used in similar sockets.

• Renesas HA-2556: Another 4-quadrant analog multiplier option.

• Burr-Brown (TI) MPY100: Legacy alternative.

• High-Precision Upgrade:

• Analog Devices AD534: Offers higher precision and lower trim errors but at a higher cost.

• Cost-Effective/Maker Options:

• Basic "Euro-rack" style diode ring modulators (discrete components) can substitute for the AD633 in Lo-Fi audio if cost is the only driver, though accuracy drops significantly.

6. Frequently Asked Questions (FAQ)

• Q: What is the main difference between AD633 and AD534?

• The AD534 is a higher precision, lower noise part with a different pinout. The AD633 is the low-cost, industry-standard version.

• Q: Can the AD633 be used in single-supply applications?

• Generally, no. The definition specifies a dual supply (±8V to ±18V) is required for proper 4-quadrant operation.

• Q: How do I calculate the output voltage?

• The formula is $W = \frac{(X1-X2)(Y1-Y2)}{10} + Z$. The division by 10V is the scaling factor.

• Q: Is the AD633 suitable for Arduino or STM32 interfacing?

• Directly, no. It requires analog voltages. You would need Dual DACs (Digital-to-Analog Converters) to drive the X/Y inputs from a microcontroller.

• Q: Where can I find the datasheet for the AD633?

• The official datasheet is available from Analog Devices or authorized distributors like Mouser/DigiKey.

7. Datasheets & Resources

• Official Datasheet: AD633 PDF Download

• Development Tools: Look for "Analog Multiplier Breakout" boards or generic SOIC-to-DIP adapters for testing.