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Semtech Corporation SX1781IMLTRT
- Part No.:
- SX1781IMLTRT
- Manufacturer:
- Semtech Corporation
- Package:
- 16-VQFN Exposed Pad
- Datasheet:
-
SX1781IMLTRT.pdf
- Description:
- IC FREQ SYNTH 16MLPQ
- Quantity:
- Payment:
- Shipping:
Inventory:1,133
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Product details
Overview
SX1781IMLTRT from Semtech is an integer-N PLL frequency synthesizer with integrated VCO, designed as a local oscillator in superheterodyne transceivers. It delivers 1200–1400 MHz RF output with ≤350 µs hopping time, −85 dBc/Hz phase noise at 10 kHz offset, and programmable +5 dBm differential output power. It operates from 3.0–3.6 V across −40 to +85°C and features SPI interface, lock detect (LD), and ultra-low-power sleep mode.
For engineers reviewing the SX1781IMLTRT datasheet, pinout, applications, or equivalent options, key selection criteria include its integrated loop filter/VCO architecture, 250 kHz minimum frequency step, complementary RF outputs (Out_P/Out_N), and squelch-enabled lock-synchronized RF enable functionality.
Technical Context
The SX1781IMLTRT implements a fully integrated integer-N PLL with on-die VCO tank and passive loop filter, eliminating external tuning components. Its PFD update frequency is fixed near 500 kHz via R-divider programming, and closed-loop bandwidth is preset at 50 kHz - not user-adjustable.
It supports dual RF output configurations: single-ended (−1 dBm into 50 Ω) or balun-combined differential (up to +5 dBm), with programmable output buffer current (3.5–11 mA). Lock detection drives LD pin high and can gate RF outputs via internal squelch logic controlled by RegGenCtrl bit [3].
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Frequency Range | 1200–1400 MHz - covers full L-band for wireless infrastructure and point-to-point radios |
| Frequency Step Size | 250 kHz min. - enables fine channel spacing compliant with narrowband standards |
| Phase Noise @ 10 kHz | −85 dBc/Hz typical - meets stringent spectral purity requirements for adjacent-channel rejection |
| Hopping Time | ≤350 µs to LD rising edge - supports fast frequency agility in TDD/FDD reconfiguration |
| Supply Voltage | 3.0–3.6 V - compatible with standard 3.3 V digital supply rails without level-shifting |
| Operating Temperature | −40 to +85°C - qualified for industrial and outdoor base station environments |
| Package | 4 × 4 mm MLPQ16 - surface-mount, thermally enhanced QFN with exposed ground pad |
Pinout & Package
The SX1781IMLTRT uses a 4 × 4 mm MLPQ16 package with exposed thermal pad (to be soldered to PCB ground for optimal thermal dissipation). Pin 1 is VDDD; pin 16 is LD (active-high lock detect).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VDDD, VDDA, VDDF | Power Supplies | Separate analog (VDDA), digital (VDDD), and synthesizer (VDDF) rails reduce supply coupling and improve phase noise |
| VSSA, VSSD, VSSF | Ground Returns | Dedicated analog/digital/synthesizer ground pins minimize return-path crosstalk |
| CLK | Reference Input | Accepts 0.5–26 MHz CMOS or AC-coupled sine input; requires TCXO-grade source for optimal phase noise |
| CSB, SCK, MOSI, MISO | SPI Interface | 16-bit slave SPI bus (≤20 MHz) for programming N/R dividers, squelch, and output current |
| Out_P / Out_N | RF Outputs | Differential 50 Ω outputs support single-ended use (−1 dBm) or balun-combined +5 dBm operation |
| LD | Lock Detect Output | Active-high open-drain signal synchronized to PLL lock; enables hardware-triggered squelch |
| SLEEPB | Deep Sleep Control | Active-low input reduces current to ≤3 µA; RF and PLL disabled while retaining register state |
Key Features
| Feature | Design Value |
|---|---|
| Integrated VCO + Loop Filter | Eliminates external tank inductors/capacitors and loop filter components - reduces BOM count and layout sensitivity |
| Complementary RF Outputs | Out_P/Out_N pair enables either single-ended use or balun-combined +5 dBm - avoids external power combiners |
| Squelch-Controlled RF Enable | LD pin directly gates RF buffers; prevents spurious emissions during unlock - no firmware polling required |
| Ultra-Low Sleep Current | ≤3 µA standby draw - extends battery life in portable or duty-cycled RF systems |
| Programmable Output Power | Four buffer current settings (3.5/5/7.5/11 mA) allow trade-off between output power and supply current |
Applications
| Wireless Base Station LO | Point-to-Point Radio Synthesizer |
|---|---|
Use Scenario: Local oscillator in 1.2–1.4 GHz FDD/TDD basestation transceivers requiring rapid channel switching and low phase noise. IC Role / Device Role / Timing Role: Generates stable, agile RF carrier with <350 µs hop time and −85 dBc/Hz phase noise for upconversion/downconversion. Use Value: Integrated VCO/filter eliminates tuning drift over temperature; squelch prevents unlocked transmission bursts. | Use Scenario: Frequency synthesizer in licensed 1.3 GHz backhaul radios where spectral purity and EVM compliance are critical. IC Role / Device Role / Timing Role: Provides clean, low-spur LO signal with −67 dBc reference spurs and <4 ps integrated jitter (100 Hz–100 kHz). Use Value: Differential outputs reduce common-mode noise; balun-combined +5 dBm drives mixer without external amplification. |
| ISM Band Transceiver LO | Test Equipment Local Oscillator |
Use Scenario: LO generation in 1.2–1.4 GHz ISM band equipment (e.g., medical telemetry, industrial sensors) operating in harsh thermal environments. IC Role / Device Role / Timing Role: Delivers stable RF output across −40 to +85°C with no external calibration; SPI-programmable for multi-channel hopping. Use Value: 4×4 mm MLPQ16 package enables compact RF front-end layout; separate VDDA/VSSA suppresses digital noise coupling. | Use Scenario: Programmable LO source in benchtop RF signal generators or spectrum analyzer local oscillators requiring fast settling and low phase noise. IC Role / Device Role / Timing Role: Functions as a digitally tuned, low-jitter clock source with precise 250 kHz frequency resolution and repeatable lock timing. Use Value: LD pin provides deterministic lock confirmation for automated test sequencing; SPI interface allows remote configuration via host controller. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar PLL synthesizer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LMX2531LQ1725E/NOPB | Wider 2.2–2.5 GHz range; fractional-N architecture; higher 3.3 V supply current (22 mA typical) | Supports wider IF/RF bands but lacks integrated loop filter - requires external components | Choose when broader frequency coverage or fractional-N flexibility outweighs integration and power advantages of SX1781IMLTRT |
| ADF4350BCPZ | 35–4400 MHz range; integrated VCO + fractional-N PLL; higher phase noise (−80 dBc/Hz @ 10 kHz) | Enables direct synthesis to higher frequencies but consumes more power (120 mW typical vs. 95 mW) | Prefer when multi-band operation or wideband sweep capability is needed, accepting higher noise and layout complexity |
Compared with LMX2531LQ1725E/NOPB and ADF4350BCPZ, the SX1781IMLTRT offers superior integration (no external loop filter), lower power (95 mW typical), and better phase noise in its native 1.2–1.4 GHz band - making it optimal for cost- and size-constrained L-band infrastructure.
Availability
SX1781IMLTRT is available at Aetrix Electronics and suitable for wireless base station LO, point-to-point radio synthesizer, ISM band transceiver LO, and test equipment local oscillator applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.
Supply support for SX1781IMLTRT 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
Semtech Corporation designs high-performance analog and mixed-signal semiconductors for advanced communications, sensing, and power management applications.
The SX1781IMLTRT belongs to Semtech's Advanced Communications & Sensing product line, engineered specifically for low-phase-noise, integrated PLL synthesizers in wireless infrastructure and licensed radio systems.
FAQ
What is the minimum frequency step size supported by the SX1781IMLTRT?
The SX1781IMLTRT supports a minimum frequency step size of 250 kHz. This is achieved by setting the PFD update frequency near 500 kHz and using the 10-bit N-divider and 6-bit R-divider registers. The step size is derived from FREF/(Rdiv+1), and the datasheet confirms 250 kHz as the smallest achievable increment under recommended operating conditions. This resolution meets narrowband channel spacing requirements in L-band wireless systems.
How does the squelch function operate in the SX1781IMLTRT?
The squelch function in the SX1781IMLTRT uses the LD (lock detect) pin to gate the RF output buffers. When enabled (default state, RegGenCtrl bit [3] = 0), RF outputs remain disabled until LD goes high, preventing spurious emissions during unlock. This hardware-level control eliminates software polling delays and ensures emission integrity. The squelch can be disabled via SPI to allow unconditional RF output, but SX1781IMLTRT's default behavior prioritizes spectral cleanliness during frequency transitions.
Can the SX1781IMLTRT generate +5 dBm output power in single-ended mode?
No, the SX1781IMLTRT cannot deliver +5 dBm in single-ended mode. Its maximum single-ended output is −1 dBm into 50 Ω (per Table 7). The +5 dBm rating applies only when Out_P and Out_N are combined using an external lumped-element balun, as detailed in Figure 5 and Page 12. Attempting to achieve +5 dBm without proper differential combining will result in degraded matching, increased harmonics, and potential instability - so SX1781IMLTRT requires the balun configuration to reach its rated high-power mode.
What is the purpose of the three separate power supply pins (VDDA, VDDD, VDDF) on the SX1781IMLTRT?
The SX1781IMLTRT uses VDDA (analog output buffers), VDDD (digital logic), and VDDF (synthesizer core) to isolate noise-sensitive circuit blocks. This separation minimizes digital switching noise coupling into the VCO and RF paths, directly improving phase noise performance. Each rail has dedicated ground returns (VSSA/VSSD/VSSF), and the datasheet specifies independent current draws (IDDA, IDDD, IDDF) - confirming that SX1781IMLTRT's architecture relies on this partitioning to meet its −85 dBc/Hz phase noise target.
Is the SX1781IMLTRT pin-compatible with any other Semtech synthesizers?
No documented pin-compatible replacements exist for the SX1781IMLTRT within Semtech's portfolio. Its 16-pin MLPQ package, pin assignment (e.g., CLK on pin 2, LD on pin 16, SLEEPB on pin 15), and functional allocation (separate VDDA/VDDD/VDDF, dual RF outputs) are unique to this device. While other Semtech synthesizers like the SX125x series share SPI interface and lock detect concepts, their pinouts, supply schemes, and RF architectures differ significantly - meaning board redesign is required when substituting. SX1781IMLTRT's layout must be implemented per its specific land pattern and thermal pad grounding requirements.
SX1781IMLTRT Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Semtech Corporation
- Series:
- -
- Package/Case:
- 16-VQFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Programmable:
- Not Verified
- Type:
- Frequency Synthesizer (RF)
- PLL:
- Yes
- Input:
- Clock
- Output:
- Clock
- Number of Circuits:
- 1
- Ratio - Input:Output:
- 1:1
- Differential - Input:Output:
- No/Yes
- Frequency - Max:
- 1.4GHz
- Divider/Multiplier:
- Yes/No
- Voltage - Supply:
- 3V ~ 3.6V
- Operating Temperature:
- -40°C ~ 85°C
- Mounting Type:
- Surface Mount
- Grade:
- -
- Qualification:
- -
- Supplier Device Package:
- 16-MLPQ (4x4)
SX1781IMLTRT FAQ
1.How can I place an order for SX1781IMLTRT through Aetrix?
Please submit a Request for Quotation (RFQ) for SX1781IMLTRT on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for SX1781IMLTRT reliable?
The price and inventory of SX1781IMLTRT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SX1781IMLTRT is usually 5 days.
3.What payment methods are accepted for SX1781IMLTRT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SX1781IMLTRT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SX1781IMLTRT?
SX1781IMLTRT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SX1781IMLTRT order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for SX1781IMLTRT?
For technical support, including SX1781IMLTRT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SX1781IMLTRT requirements.
6.How does Aetrix verify that SX1781IMLTRT is sourced from the original manufacturer or authorized distributors?
All SX1781IMLTRT products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SX1781IMLTRT meets industry standards.
7.What is the process for return or replacement of SX1781IMLTRT?
All SX1781IMLTRT units undergo pre-shipment inspection (PSI). If there is an issue with SX1781IMLTRT, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The SX1781IMLTRT part is unused and in its original packaging.
Return procedure for SX1781IMLTRT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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