Analog Devices Inc. AD9821KST

Overview

AD9821KST from Analog Devices is a complete 12-bit, 40 MSPS imaging signal processor designed for CMOS and CCD imagers with on-chip correlated double sampling (CDS). It integrates a differential sample-and-hold amplifier (SHA), 0 dB to 36 dB digitally controlled VGA, optical black clamp circuit, and 12-bit ADC - all operating from a single 3 V supply with 150 mW typical power consumption.

For engineers reviewing the AD9821KST datasheet, AD9821KST pinout, AD9821KST application, or AD9821KST equivalent, this device serves as a dedicated analog front-end (AFE) for digital still cameras and industrial/scientific imaging systems requiring precise gain control, black-level correction, and high-speed digitization without external CDS.

Technical Context

The AD9821KST implements a single-channel imager signal chain optimized for non-CDS imagers: differential SHA samples VIN+ and VIN– simultaneously on DATACLK rising edges (3 ns aperture delay), followed by 10-bit VGA with linear-in-dB gain curve (0.0351 dB/LSB), then optical black clamp using CLPOB-synchronized feedback to an 8-bit DAC, and finally 12-bit ADC with 2.0 V full-scale range and straight binary output coding.

Configuration and calibration are managed via a 3-wire serial interface (SCK, SDATA, SL) supporting register read/write at up to 10 MHz; internal registers control VGA gain (1024 steps), clamp level (256 steps), power-down modes (standby: 5 mW; total power-down: 1 mW), and DATACLK/CLPOB polarity.

Key Specifications

Pinout & Package

AD9821KST is housed in a 48-lead LQFP (ST-48) package with 0.5 mm pitch and 7 mm × 7 mm body size, compliant with JEDEC MS-026BBC. Thermal resistance θ_JA = 56°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar imaging signal processor applications.

Compared with AD9822KST, AD9821KST reduces component count and board area for single-sensor applications; compared with TDA8785H/N1, it provides superior noise performance (0.5 LSB_rms vs. ~1.2 LSB_rms) and 3 V operation essential for portable medical and consumer imaging.

Availability

AD9821KST is available at Aetrix Electronics and suitable for digital still cameras, industrial machine vision systems, scientific imaging platforms, and medical endoscopy devices requiring stable component supply and long-term manufacturability.

Supply support for AD9821KST includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices, Inc. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Norwood, MA, with design centers worldwide.

The AD9821KST belongs to Analog Devices' Imaging Signal Processor product line, engineered specifically for high-fidelity, low-power analog signal conditioning in CMOS and CCD-based imaging systems where on-chip CDS is present.

FAQ

What is the primary function of the AD9821KST in an imaging system?

The AD9821KST serves as a complete analog front-end (AFE) for CMOS and CCD imagers with on-chip correlated double sampling (CDS). Its core functions include differential sample-and-hold, 0 dB to 36 dB variable gain amplification, optical black level clamping, and 12-bit 40 MSPS analog-to-digital conversion - all integrated into a single 48-lead LQFP package. The AD9821KST eliminates the need for discrete signal conditioning components while maintaining high linearity and low noise for precision imaging applications.

Does the AD9821KST require external CDS circuitry?

No, the AD9821KST is explicitly designed for use with CMOS imagers and CCD arrays that already incorporate on-chip correlated double sampling (CDS). It does not include CDS functionality itself; instead, it processes the CDS-conditioned analog output through its VGA, clamp, and ADC stages. The AD9821KST's optical black clamp corrects residual offsets and low-frequency drift after CDS, making external CDS unnecessary and reducing system complexity.

How is gain controlled on the AD9821KST, and what is its resolution?

Gain on the AD9821KST is controlled digitally via a 10-bit VGA gain register accessible through its 3-wire serial interface (SCK, SDATA, SL). The gain range spans 0 dB to 36 dB in 1024 monotonic steps, with each step corresponding to approximately 0.0351 dB. This linear-in-dB characteristic allows precise, repeatable gain adjustment across lighting conditions - a capability confirmed in Figure 11 and Table III of the AD9821KST datasheet.

What are the power supply requirements for the AD9821KST?

The AD9821KST operates from a single 3 V nominal supply, with allowable voltage ranges of 2.7 V to 3.6 V for AVDD, DVDD, and DRVDD rails. It features separate analog (AVDD1/AVDD2), digital (DVDD1/DVDD2), and digital driver (DRVDD) supplies to minimize noise coupling. At 40 MSPS, typical power dissipation is 150 mW; standby mode reduces consumption to 5 mW, and total power-down lowers it to 1 mW - all verified in the Imager-Mode Specifications table.

Can the AD9821KST interface directly with a 2.7 V ASIC or FPGA?

Yes, the AD9821KST supports interfacing with 2.7 V logic devices via its dedicated DRVDD supply pin (Pin 13), which can be set to 2.7 V independently of the 3 V DVDD rail. Digital outputs D0–D11 are driven from DRVDD/DRVSS, enabling level compatibility with 2.7 V ASICs while maintaining noise isolation from the main digital supply. This configuration is explicitly recommended in the Grounding and Decoupling section of the AD9821KST datasheet.