AD8328ACPZ-REEL7

Overview

The AD8328 is a 5 V upstream cable line driver designed for DOCSIS and EuroDOCSIS reverse path transmission. It features digitally programmable gain over a 59 dB range with 1 dB steps via an SPI interface. The device supports differential or single-ended inputs, maintaining a 300 Ω output impedance that matches 75 Ω loads through a 2:1 transformer. Key performance metrics include -57.5 dBc SFDR at 21 MHz and -54 dBc at 65 MHz, with an upper bandwidth of 107 MHz across the full gain range.

Feature Summary

• Digital gain control via SPI interface with 1 dB step resolution
• Maintains consistent 75 Ω output impedance in both transmit enable and disable states
• Integrated sleep mode reducing quiescent current to 20 μA
• Optimized low distortion performance for QPSK and QAM modulation schemes

Applications

• DOCSIS and EuroDOCSIS cable modems
• CATV set-top boxes
• CATV telephony modems
• Coaxial and twisted pair line drivers

Procurement Notes

Verify component authenticity through authorized Analog Devices distributors or direct manufacturer channels. Confirm package type (LFCSP or QSOP) and temperature grade (-40°C to +85°C) against specific design requirements. Check for obsolete status indicators as the datasheet marks this part as obsolete; ensure availability of long-term supply agreements or alternative sourcing strategies if required for production.

Selection Notes

Select the AD8328 for applications requiring precise digital gain control in upstream cable transmission systems. Ensure the design accommodates a 5 V single supply and utilizes a 2:1 output transformer for proper impedance matching. Consider the thermal characteristics of the LFCSP versus QSOP package based on board layout constraints. Verify that the host microcontroller can support the required SPI timing parameters for reliable data transfer.

Part Context

The AD8328 belongs to Analog Devices' lineup of coaxial line drivers tailored for cable modem infrastructure. It serves as a power amplifier stage in reverse path transmission, bridging digital signal processors or DACs with the cable network. Its integration of high-linearity amplification and digital control simplifies the design of compliant DOCSIS upstream paths.

Replacement Considerations

No public confirmed substitutes are listed in the provided documentation. As the datasheet indicates the part is obsolete, engineers should consult Analog Devices for current replacement recommendations or evaluate equivalent products from other manufacturers that meet DOCSIS specifications.

FAQ

How does the AD8328 maintain output impedance during transmit disable?

The AD8328 maintains a differential output impedance of 300 Ω regardless of whether the transmitter is enabled or disabled. This allows it to match a 75 Ω load using a 2:1 transformer without requiring external back-termination resistors.

What is the function of the RAMP pin?

The RAMP pin controls the duration of burst on/off transients. Leaving it unconnected ensures compliance with DOCSIS 2.0 spurious emission requirements by limiting transient dissipation time to no faster than 2 μs.

Can the AD8328 accept single-ended input signals?

Yes, the AD8328 accepts either differential or single-ended input signals. For single-ended operation, the input impedance is approximately 800 Ω, while differential input impedance is 1.6 kΩ.