**AD835AN: A Comprehensive Guide to the 250 MHz Voltage Output Analog Multiplier**

The **AD835AN** is a high-performance, monolithic **analog multiplier** from Analog Devices, renowned for its precision and speed in a wide array of signal processing applications. As a **voltage-output device**, it simplifies system design by providing a straightforward interface, eliminating the need for external operational amplifiers in many configurations. Its defining characteristic is an impressive **250 MHz bandwidth**, making it a cornerstone component in high-frequency circuits where accurate multiplication of analog signals is paramount.

**Core Architecture and Operation**

The AD835AN is built on a sophisticated **translinear core** architecture, which ensures excellent temperature stability and linearity. It operates on the fundamental principle of the Gilbert cell but is optimized for enhanced performance. The multiplier implements the function:

`W = (X1 – X2)(Y1 – Y2)/U + Z`

Where `W` is the output, and `X`, `Y` are the differential input voltages. The `U` term is a scaling factor, typically set to 1 V by an internal reference, and the `Z` input allows for addition or offset adjustment. In its most common single-ended use case, the function simplifies to `W = (X * Y) + Z`, providing an intuitive and powerful building block for designers.

**Key Features and Specifications**

* **High Bandwidth:** The **250 MHz small-signal bandwidth** and **1000 V/µs slew rate** enable the processing of very fast signals with minimal distortion, crucial for RF and video applications.

* **Excellent Accuracy:** It boasts low multiplicative error (typically ±0.5%) and low drift, ensuring reliable performance over time and temperature variations.

* **Versatile Power Supply:** It operates from dual supplies ranging from ±5 V to ±18 V, offering flexibility for different system voltage levels.

* **Low Power Consumption:** Despite its high speed, the device consumes a modest 20 mA of supply current, making it suitable for power-sensitive designs.

* **Robust Output Drive:** The voltage output can drive loads as low as 25 Ω, allowing it to directly drive cables, filters, or subsequent ADC stages.

**Primary Applications**

The combination of speed and precision opens the door to numerous advanced applications:

* **Modulation/Demodulation:** It is ideal for amplitude modulation (AM), double-sideband suppressed-carrier (DSB-SC) modulation, and synchronous demodulation schemes.

* **Phase Detection and Frequency Doubling:** Used in phase-locked loops (PLLs) and for generating second harmonics in frequency doubler circuits.

* **Automatic Gain Control (AGC):** It can form the heart of a high-speed AGC loop by multiplying the input signal with a control voltage.

* **Voltage-Controlled Amplifiers (VCA) and Filters:** One input can serve as the signal path while the other acts as a gain control input, creating a wideband VCA.

* **Square Root and Squaring Circuits:** When connected in a feedback configuration with an op-amp, it can efficiently perform squaring and square root functions.

**Design Considerations**

To achieve the datasheet performance, careful design and layout are essential:

1. **Bypassing:** Use high-frequency decoupling techniques. Place **0.1 µF ceramic capacitors** as close as possible to the power supply pins and larger (10 µF) tantalum capacitors nearby to suppress low-frequency noise.

2. **Grounding:** Implement a solid, low-impedance ground plane to minimize noise and ensure signal integrity.

3. **Input/Output Matching:** For very high-frequency applications, proper termination of inputs and outputs may be necessary to prevent signal reflections.

4. **Heat Dissipation:** While not a high-power device, the AD835AN is offered in an 8-pin PDIP package. In elevated temperature environments, ensuring adequate airflow is recommended.

ICGOODFIND: The **AD835AN** stands as a versatile and robust solution for high-speed analog computation. Its **exceptional 250 MHz bandwidth**, combined with its voltage-output architecture and ease of use, makes it an indispensable component for engineers designing RF systems, precision instrumentation, and advanced signal processing chains. Its enduring popularity is a testament to its reliable performance and the critical role it plays in analog design.

**Keywords:** Analog Multiplier, 250 MHz Bandwidth, Voltage Output, High-Frequency Signal Processing, AD835AN