DATA SHEET SKY72300-21: Spur-Free, 2.1 GHz Dual Fractional-N Frequency Synthesizer Applications x Direct digital modulation x General purpose RF systems x 3 V operation x 2.5G and 3G wireless infrastructure x 5 V output to loop filter x Broadband wireless access x EP-TSSOP (28-pin, 9.7 x 6.4 x 1.1 mm) package (MSL3, 260 qC x Low bit rate wireless telemetry per JEDEC J-STD-020) x Instrumentation x L-band receivers Description x Satellite communications Skyworks SKY72300-21 direct digital modulation fractional-N frequency synthesizer provides ultra-fine frequency resolution, fast switching speed, and low phase-noise performance. This Features synthesizer is a key building block for high-performance radio system designs that require low power and fine step size. x Spur-free operation The ultra-fine step size of less than 100 Hz allows this synthesizer x 2.1 GHz maximum operating frequency to be used in very narrowband wireless applications. With proper x 500 MHz maximum auxiliary synthesizer temperature sensing or through control channels, the synthesizer’s fine step size can compensate for crystal oscillator x Ultra-fine step size, 100 Hz or less or Intermediate Frequency (IF) filter drift. As a result, crystal x High internal reference frequency enables large loop bandwidth oscillators or crystals can replace temperature-compensated or implementations ovenized crystal oscillators, reducing parts count and associated x Very fast switching speed (e.g., below 100 Ps) component cost. The device’s fine step size can also be used for Doppler shift corrections. x Phase noise to –91 dBc/Hz inside the loop filter bandwidth @ 1800 MHz The SKY72300-21 has a phase noise floor of –90 dBc/Hz up to 2.1 GHz operation as measured inside the loop bandwidth. This is x Software programmable power-down modes permitted by the on-chip low noise dividers and low divide ratios x High-speed serial interface up to 100 Mbps provided by the device’s high fractionality. x Three-wire programming Reference crystals or oscillators up to 50 MHz can be used with x Programmable division ratios on reference frequency the SKY72300-21. The crystal frequency is divided down by independent programmable dividers (1 to 32) for the main and x Phase detectors with programmable gain to provide a programmable loop bandwidth auxiliary synthesizers. The phase detectors can operate at a maximum speed of 25 MHz, which allows better phase noise due x Frequency power steering further enhances rapid acquisition to the lower division value. With a high reference frequency, the time loop bandwidths can also be increased. Larger loop bandwidths x On-chip crystal oscillator improve the settling times and reduce in-band phase noise. Therefore, typical switching times of less than 100 s can be x Frequency adjust for temperature compensation achieved. The lower in-band phase noise also permits the use of lower cost Voltage Controlled Oscillators (VCOs) in customer Skyworks offers lead (Pb)-free RoHS (Restriction of applications. Hazardous Substances) compliant packaging. Innovation to GoTM Now available for purchase online. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 101217N • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • September 11, 2009 1 DATA SHEET • SKY72300-21 FREQUENCY SYNTHESIZER The SKY72300-21 has a frequency power steering circuit that This capability can eliminate the need for In-phase and helps the loop filter to steer the VCO when the frequency is too Quadrature (I/Q) Digital-to-Analog Converters (DACs), quadrature fast or too slow, further enhancing acquisition time. upconverters, and IF filters from the transmitter portion of the The unit operates with a three-wire, high-speed serial interface. A radio system. combination of large bandwidth, fine resolution, and the three- Figure 1 shows a functional block diagram for the SKY72300-21. wire, high-speed serial interface allows for a direct frequency The device package and pinout for the 28-pin Exposed Pad Thin modulation of the VCO. This supports any continuous phase, Shrink Small Outline Package (EP-TSSOP) are shown in Figure 2. constant envelope modulation scheme such as Frequency Modulation (FM), Frequency Shift Keying (FSK), Minimum Shift Keying (MSK), or Gaussian Minimum Shift Keying (GMSK). Data Registers Clock Main PD/Charge Pump Serial Modulation Main Modulation Ref Freq Aux Aux CS Data MSB/LSB Divider Control Dividers Divider & Pwr-Dn/Mux Out Dividend Interface Dividend Control Mod_in Modulation Unit Mux Mux_out ΔΣ ΔΣ 18-Bit 10-Bit Fractional Fractional Unit Reference Unit Frequency Oscillator Fvco_main Fvco_aux Main Main Auxiliary Auxiliary Fvco_main Divider Divider Divider Prescaler Fvco_aux Fpd_mainFref_main Fref_aux Fpd_aux Main Auxiliary Phase/Freq. Phase/Freq. Detector Fref Detector and and Charge Pump Reference Charge Pump Frequency Oscillator CPout_main CPout_aux Lock Detection or LD/PSmain LD/PSaux Lock Detection or Power Steering Power Steering C1447 Figure 1. SKY72300-21 Functional Block Diagram Clock 1 28 CS Mod_in 2 27 Data Mux_out 3 26 VCCdigital VSUBdigital 4 25 GNDdigital GNDcml 5 24 VCCcml_aux VCCcml_main 6 23 VCCvco_aux Fvco_main 7 22 Fvco_aux Fvco_main 8 21 GNDcp_aux LD/PSmain 9 20 CPout_aux VCCcp_main 10 19 VCCcp_aux CPout_main 11 18 LD/PSaux GNDcp_main 12 17 GNDxtal Xtalacgnd/OSC 13 16 VCCxtal Xtalin/OSC 14 15 Xtalout/NC C1412 Figure 2. SKY72300-21 Pinout, 28-Pin EP-TSSOP (Top View) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 2 September 11, 2009 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 101217N DATA SHEET • SKY72300-21 FREQUENCY SYNTHESIZER Technical Description 38 to 537 are possible in fractional-N mode and from 32 to 543 in The SKY72300-21 is a fractional-N frequency synthesizer using a integer-N mode. '6 modulation technique. The fractional-N implementation provides low in-band noise by having a low division ratio and fast Reference Frequency Oscillator frequency settling time. In addition, the SKY72300-21 provides The SKY72300-21 has a self-contained, low-noise crystal arbitrarily fine frequency resolution with a digital word, so that the oscillator. This crystal oscillator is followed by the clock frequency synthesizer can be used to compensate for crystal generation circuitry that generates the required clock for the frequency drift in the RF transceiver. programmable reference frequency dividers. Serial Interface Reference Frequency Dividers The serial interface is a versatile three-wire interface consisting of The crystal oscillator signal can be divided by a ratio of 1 to 32 to three pins: Clock (serial clock), Data (serial input), and CS (chip create the reference frequencies for the phase detectors. The select). It enables the SKY72300-21 to operate in a system where SKY72300-21 has both a main and an auxiliary frequency one or multiple masters and slaves are present. To perform a synthesizer, and provides independently configurable dividers of loopback test at startup and to check the integrity of the board the crystal oscillator frequency for both the main and auxiliary and processor, the serial data is fed back to the master device phase detectors. The divide ratios are programmed by the (e.g., a microcontroller or microprocessor unit) through a Reference Frequency Dividers Register. programmable multiplexer. This facilitates hardware and software debugging. NOTE: The divided crystal oscillator frequencies (which are the internal reference frequencies), Fref_main and Fref_aux, Registers are referred to as reference frequencies throughout this There are ten 16-bit registers in the SKY72300-21. For more document. information, see the Register Descriptions section of this document. Phase Detectors and Charge Pumps The SKY72300-21 uses a separate charge pump phase detector Main and Auxiliary '6 Modulators for each synthesizer which provides a programmable gain, Kd, The fractionality of the SKY72300-21 is accomplished by the use from 31.25 to 1000 PA/2S radians in 32 steps programmed using of a proprietary, configurable 10-bit or 18-bit '6 modulator for the Phase Detector/Charge Pump Control Register. the main synthesizer and 10-bit '6 modulator for the auxiliary synthesizer. Frequency Steering When programmed for frequency power steering, the SKY72300- Main and Auxiliary Fractional Units 21 has a circuit that helps the loop filter steer the VCO, through The SKY72300-21 provides fractionality through the use of main the LD/PSmain signal (pin 9). In this configuration, the LD/PSmain and auxiliary '6 modulators. The output from the modulators is signal can provide for more rapid acquisition. combined with the main and auxiliary divider ratios through their When programmed for lock detection, internal frequency steering respective fractional units. is implemented and provides frequency acquisition times comparable to conventional phase/frequency detectors. VCO Prescalers The VCO prescalers provide low-noise signal conditioning of the Lock Detection VCO signals. They translate from an off-chip, single-ended or When programmed for lock detection, the SKY72300-21 provides differential signal to an on-chip differential Current Mode Logic an active low, pulsing open collector output using the LD/PSmain (CML) signal. The SKY72300-21 has independent main and signal (pin 9) to indicate the out-of-lock condition. When locked,