Asahi Kasei Microdevices/AKM AK1590

Overview

AK1590 from Asahi Kasei is a Delta-Sigma Fractional-N PLL frequency synthesizer IC designed for RF signal generation in wireless infrastructure and test equipment. It delivers 60–1000 MHz output with −201 dBc/Hz phase noise, 24-pin QFN package, and dual charge pumps enabling fast lockup (≤100 µs typical). Its role is to generate stable, programmable local oscillator signals in transceivers requiring high spectral purity and rapid frequency switching.

For engineers reviewing the AK1590 datasheet, AK1590 pinout, AK1590 application, or AK1590 equivalent, key selection considerations include its 18-bit delta-sigma modulator resolution, 2.5 mA typical supply current at 3.3 V, Fast Lockup mode timing control via register , and dual-mode lock detect (analog/digital) configurable via LDCKSEL bits.

Technical Context

The AK1590 implements a fractional-N architecture with an 18-bit delta-sigma modulator and dual-modulus prescaler (4/5, 8/9, 16/17), supporting integer + fractional division to achieve fine frequency resolution. Its phase detector operates at up to 125 MHz input frequency, and it accepts reference inputs from 5–40 MHz with programmable R-divider (4–255).

It integrates two independent charge pumps: Charge Pump 1 (20–168 µA, 8-step programmable) for normal operation and Charge Pump 2 (0.84–2.32 mA, 8-step) for Fast Lockup mode, triggered by {FASTEN}=1 and timed via 13-bit FAST[12:0] counter. The loop filter connects externally to CP, CPZ, and SWIN pins, with CPZ requiring connection even when Fast Lockup is disabled.

Key Specifications

Pinout & Package

AK1590 uses a 24-pin QFN package (4 mm × 4 mm × 0.7 mm, 0.5 mm pitch) with exposed thermal pad connected to ground. Pin functions are validated per MS1478-E-02 Rev. 2 (2015).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fractional-N PLL synthesizer applications.

Compared with LMX2594 and ADF4355, the AK1590 offers superior phase noise performance and deterministic Fast Lockup timing control at lower quiescent current, making it optimal for high-fidelity narrowband LO generation where external VCO flexibility and low power are critical.

Availability

AK1590 is available at Aetrix Electronics and suitable for wireless infrastructure, RF test equipment, automated calibration systems, and spectrum analysis requiring stable component supply with long-term lifecycle support.

Supply support for AK1590 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

Asahi Kasei Microdevices (AKM) is a Japanese semiconductor company specializing in mixed-signal ICs for audio, sensor, and precision timing applications, with over 30 years of analog design heritage.

The AK1590 belongs to AKM's high-performance RF synthesizer product line, engineered specifically for low-phase-noise, fast-locking local oscillator generation in communications and instrumentation systems.

FAQ

What is the maximum reference input frequency supported by the AK1590?

The AK1590 supports reference input frequencies from 5 MHz to 40 MHz, as specified in the Recommended Operating Range (Table 3) and Electrical Characteristics (Section 7.3). This range accommodates common crystal oscillator outputs and buffered clock sources without requiring external division. The R-divider register ( R[7:0]) allows further scaling down the reference to set the phase detector frequency, which directly impacts lock time and loop stability.

How does the Fast Lockup mode function in the AK1590?

The AK1590 Fast Lockup mode activates Charge Pump 2 (0.84–2.32 mA) for rapid initial lock, then switches back to Charge Pump 1 (20–168 µA) for low-noise steady-state operation. It is enabled by setting D[16]={FASTEN}=1 in , and triggered by either a frequency change or PDN2 transition from Low to High. The duration is precisely controlled by the 13-bit FAST[12:0] counter, defining the number of PFD cycles the high-current pump remains active.

Can the AK1590 operate with a single 3.3 V supply?

Yes, the AK1590 supports single-supply operation at 3.3 V applied to both PVDD and CPVDD pins, as confirmed in Table 3 (Recommended Operating Range). PVDD supplies peripherals (2.7–5.5 V), and CPVDD supplies the charge pump (up to 5.5 V). Using 3.3 V for both simplifies power design while maintaining full functionality, including Fast Lockup mode and all register configurations, with typical current draw of 2.5 mA.

What is the purpose of the OFFSET register in the AK1590?

The OFFSET register () provides 18-bit signed frequency offset adjustment, enabling real-time carrier trimming without recalculating the main numerator. It adds directly to NUM[17:0] in the delta-sigma modulator path. When used, DITH must be set to 0 (OFF) to prevent instability. This feature is essential for calibration loops, DC offset correction in I/Q modulators, and fine-tuning against metrology references-functions explicitly documented in Section 10 of the AK1590 datasheet.

How is lock detection implemented in the AK1590?

The AK1590 offers two lock detection modes selectable via D[11]={LD} in . Digital Lock Detect asserts LD=High after 63 consecutive phase-error measurements below a user-configurable threshold (1×, 2×, or 3× REFIN period), while Analog Lock Detect outputs the raw PFD comparison result on the LD pin. The choice affects system response time and diagnostic capability: digital mode gives clean status signaling; analog mode enables oscilloscope-based PFD waveform analysis during development.