1.0625Gbps to 11.3Gbps, SFP+ Dual-Path Limiting Amplifier

1Gbps to 11Gbps Limiting Amp Enables < 1W SFP+ Optical Transceiver Modules

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The MAX3945 is a +3.3V, multirate, low-power limiting amplifier optimized for Fibre Channel and Ethernet transmission systems at data rates up to 11.3Gbps. The high-sensitivity limiting amplifier limits the signal generated by a transimpedance amplifier into a CML-level differential output signal. All differential inputs and outputs (I/O) are optimally back terminated for 50Ω transmission line PCB design. The MAX3945's dual-path limiting amplifier has programmable filtering to optimize sensitivity for different data rates and to suppress relaxation oscillations that could occur in some optical systems. The MAX3945 incorporates two loss-of-signal (LOS) circuits and a programmable time mask for the LOS output.

A 3-wire digital interface reduces the pin count and enables control of LOS threshold, LOS polarity, LOS mode, CML output level, input offset correction, receive (Rx) polarity, Rx input filter, and Rx deemphasis without the need for external components.

The MAX3945 is packaged in a 3mm x 3mm, 16-pin TQFN package.
MAX3945: Typical Application Circuit MAX3945: Typical Application Circuit Enlarge+

Key Features

  • 130mW Power Dissipation Enables < 1W SFP+ Modules
  • Enables Single-Module Design Compliance with 1000BASE-SX/LX and 10GBASE-SR/LR Specifications
  • -25.3dBm Optical Sensitivity at 1.25Gbps Using a 10.32Gbps ROSA
  • Selectable 1GHz/2.1GHz/2.5GHz/3GHz Input Filters at RATE_SEL = 0 Setting
  • Supports SFF-8431 SFP+ MSA and SFF-8472 Digital Diagnostic
  • Total Power Dissipation of 130mW at 3.3V Power Supply with RSSI Monitor-Based LOS
  • Total Power Dissipation of 154mW at 3.3V Power Supply with Rx Input-Based LOS
  • 4mVP-P Input Sensitivity at 11.3Gbps
  • 4psP-P DJ at 11.3Gbps with RATE_SEL = 1
  • 4psP-P DJ at 8.5Gbps with RATE_SEL = 1
  • 5psP-P DJ at 4.25Gbps with RATE_SEL = 0, BW1 = 1, BW0 = 1
  • 9.0psP-P DJ at 1.25Gbps with RATE_SEL = 0, BW1 = 0, BW0 = 0
  • 26ps Rise and Fall Time with RATE_SEL = 1
  • 52ps Rise and Fall Time with RATE_SEL = 0
  • CML Output with Level Adjustment and Squelch Mode
  • Programmable CML Output Deemphasis
  • CML Output Polarity Select
  • LOS Polarity Select
  • Programmable Masking Time for the LOS Output
  • LOS Assert/Deassert Level Adjustment
  • Choice of Rx Input-Based LOS or RSSI Monitor-Based LOS
  • 3-Wire Digital Interface Compatible with Maxim’s SFP+ Family of Products


  • 10G PON ONU
  • 10GBASE-SR/LR SFP+ Optical Transceiver
  • 1x/2x/4x/8x SFF/SFP/SFP+ MSA Fibre-Channel Optical Transceiver

See parametric specs for Limiting Amplifiers (10)

Part NumberTarget Oper. Range
Data Rate
Data Rate
I/O TypeInput Sens.
LOS Sens.
Edge Speed
minmaxtypminmaxSee Notes
MAX3945 5 to >101062113003.339CML45.135
$4.20 @1k

Pricing Notes:
This pricing is BUDGETARY, for comparing similar parts. Prices are in U.S. dollars and subject to change. Quantity pricing may vary substantially and international prices may differ due to local duties, taxes, fees, and exchange rates. For volume-specific and version-specific prices and delivery, please see the price and availability page or contact an authorized distributor.

MAX3945EVKIT: Evaluation Kit for the MAX3945
Product Reliability Reports: MAX3945.pdf 
Device   Fab Process   Technology   Sample size   Rejects   FIT at 25°C   FIT at 55°C   Material Composition  

Note : The failure rates are summarized by technology and mapped to the associated material part numbers. The failure rates are highly dependent on the number of units tested.

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