Skyworks Solutions Inc. SI4112-BM

Overview

SI4112-BM from Silicon Laboratories is a monolithic dual-band RF synthesizer with integrated VCOs, loop filters, and phase detectors for wireless communications systems. It delivers RF1 output (900 MHz–1.8 GHz), RF2 output (750 MHz–1.5 GHz), and IF output (62.5 MHz–1000 MHz) with 1 µA standby current, 18 mA typical supply current, and 2.7–3.6 V operation - used in GSM/DCS/PCS cellular transceivers.

For engineers reviewing the SI4112-BM datasheet, SI4112-BM pinout, SI4112-BM application, or SI4112-BM equivalent, this page provides verified technical context, validated pin functions, confirmed RF/IF frequency ranges, real-world powerdown behavior, and documented alternative synthesizers for multi-band wireless front-end design.

Technical Context

The SI4112-BM implements three independent PLLs - two for dual-band RF synthesis (RF1/RF2) and one for IF synthesis - each with integrated VCOs, programmable R/N dividers, and self-tuning algorithms that compensate for ±10% external inductance tolerance. Its architecture avoids fractional-N spurs while achieving <0.1 ppm frequency lock accuracy.

It uses a 3-wire serial interface (SCLK/SDATA/SEN) to configure 22-bit registers controlling VCO center frequencies, phase detector gain (4 settings), powerdown states (per-PLL), and auxiliary output selection. The self-tuning algorithm executes on power-up or frequency reprogramming, reducing initial frequency error to <1% before final PLL lock.

Key Specifications

Pinout & Package

SI4112-BM is housed in a 24-pin TSSOP package (RoHS-compliant, lead-free) with exposed thermal pad. Pin functions are electrically identical to Si4133-GT per Silicon Labs documentation, validated for RF/IF synthesis control and output routing.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-band RF synthesizer applications.

Compared with SI4112-BM, Si4133-GT offers identical functionality with updated documentation and guaranteed longevity, while MAX2870ETJ+ trades integration for broader frequency coverage and added complexity - making SI4112-BM optimal for cost-sensitive, space-constrained dual-band cellular designs.

Availability

SI4112-BM is available at Aetrix Electronics and suitable for GSM 850/PCS 1900 transceivers, DCS 1800/E-GSM 900 handsets, and wireless local loop base stations requiring stable component supply across extended product lifecycles.

Supply support for SI4112-BM 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

Silicon Laboratories is a fabless semiconductor company specializing in mixed-signal ICs for timing, wireless, and sensor applications - founded in 1996 and headquartered in Austin, Texas.

The SI4112-BM belongs to the Si41xx family of integrated RF synthesizers designed specifically for low-power, multi-band wireless communication systems where minimal external components and fast frequency switching are critical.

FAQ

What is the RF frequency coverage of the SI4112-BM?

The SI4112-BM supports dual-band RF synthesis: RF1 covers 947–1720 MHz center frequency with ±5% tuning range (effectively ~900–1800 MHz), and RF2 covers 789–1429 MHz center with ±5% tuning (effectively ~750–1500 MHz). These ranges directly support GSM 850, E-GSM 900, DCS 1800, and PCS 1900 standards. SI4112-BM achieves this using two dedicated VCOs with integrated self-tuning algorithms.

Does the SI4112-BM require external loop filters?

No, the SI4112-BM integrates all loop filter components internally - including resistors, capacitors, and charge pumps - eliminating the need for external passive loop filters. This reduces bill-of-materials count, PCB area, and calibration effort. External components are limited to VCO tank inductors (RFLx pins) and AC-coupling capacitors for RFOUT/IFOUT, as specified in the Si4133 datasheet which applies to SI4112-BM.

How does the self-tuning algorithm work in the SI4112-BM?

The SI4112-BM executes a self-tuning algorithm on power-up or after frequency reprogramming to compensate for manufacturing tolerances in external VCO inductors (±10%). It adjusts varactor bias to bring the VCO free-running frequency within <1% of target before PLL lock. This occurs in ~13 phase detector update periods, after which the PLL completes final 0.1 ppm lock in 25 additional periods - total settling time is ~40/fφ.

What package type is used for the SI4112-BM?

The SI4112-BM is packaged in a 24-pin TSSOP (Thin Shrink Small Outline Package) with exposed thermal pad, RoHS-compliant and lead-free. Its pinout matches the Si4133-GT variant exactly, including identical assignments for SCLK, SDATA, SEN, PWDN, XIN, RFOUT, IFOUT, AUXOUT, and VCO inductor terminals (RFLA–RFLD). Package dimensions and thermal characteristics are documented in Silicon Labs' Si4133-GT package outline.

Can the SI4112-BM generate IF frequencies below 100 MHz?

Yes, the SI4112-BM supports IFOUT frequencies from 62.5 MHz to 1000 MHz using its programmable ÷1/÷2/÷4/÷8 divider. At minimum division (÷8), the IF VCO center frequency of 526 MHz yields 65.75 MHz - meeting the 62.5 MHz lower bound. Output level is load-dependent; for resistive loads >500 Ω, the LPWR bit (Register 0) should be set to reduce IF amplifier bias current and optimize power efficiency.