Frequency Synthesizer Product Collection

JasonYoo

Frequency Synthesizer Product Collection [Copy link]

In the field of communications, bandwidth is everything. For wireless multimedia, instantaneous data, high voice quality and other key services, bandwidth is critical. But bandwidth is a limited resource, and we need to use advanced amplitude and phase-based modulation formats to squeeze the most information into a given frequency band. Microwave frequency synthesizers are one of the most critical components to achieve high bandwidth efficiency. Modern synthesizers use a variety of existing digital technologies to achieve the noise, stability and resolution standards required by the most modern communication systems.

Of course, frequency synthesizers come in many different shapes and sizes, from tiny system-on-chip (SoC) devices and compact modules to rugged military-grade rack-mount systems and bench-top instruments. Available frequency synthesizer technologies vary almost as much as their packaging options, including analog, digital, or a combination of the two (the latter is more common). Traditionally, frequency synthesizers have relied on a phase-locked loop (PLL) architecture that locks the phase of a tunable oscillator (such as a voltage-controlled oscillator or a YIG-tuned oscillator) to the phase of a reference source (such as an OCXO, an ovenized crystal oscillator) that has inherently high stability.

Most early SoC synthesizer designs for wireless portable devices relied on PLL architectures, using a single RF or IF synthesizer to provide the local oscillator (LO) frequency required by the wireless receiver or transmitter. Recently, leading PLL chip suppliers such as Fujitsu Microelectronics America (www.fujitsu.com) have combined multiple PLL circuits on a single chip. For example, the company's MB15U30SP is a serial-input PLL synthesizer with 2.5GHz and 510MHz prescalers that can generate output signals up to these highest frequencies. This dual PLL saves board space on an IC and is ideal for mobile communications applications that require RF and IF signals as local oscillators.

Similarly, National Semiconductor offers the LMX2364 dual frequency synthesizer for digital cellular applications, which is based on two optional frequency synthesis techniques: fractional-N and integer-N synthesis. This IC combines a 2.6GHz fractional-N synthesizer with a low-power 850MHz integer-N synthesizer. Fractional-N synthesizer technology is also the basis of the ADF4154 IC produced by Analog Devices (ADI). This single frequency synthesizer combines integer and fractional registers to produce high-resolution and low-noise output signals with a frequency range of 0.5-4.0GHz.

ADI is also a supplier of direct digital synthesis (DDS), one of the fastest growing frequency synthesis technologies. DDS technology stores digital instructions in frequency and phase accumulators and converts them into CW (continuous wave) and modulated waves through high-performance digital-to-analog converters (DACs). Based on the Nyquist theorem (the sampling frequency must be at least twice the signal frequency so that the digital code can reliably express the original signal), it is conservatively said that direct digital synthesizers can reliably generate output signals at a frequency of about 40% of the clock frequency.

For example, ADI's AD9858 is a complete direct digital synthesizer with an integral 10-bit DAC. It operates at up to 1GSps, so it can output frequencies of 400MHz or higher. Using a 32-bit frequency tuning word (FTW), the synthesizer's frequency resolution can reach less than 1Hz. The phase noise of its on-board DAC is less than -130 dBc/Hz (at a carrier offset of 1kHz). The frequency tuning and control words are loaded into the AD9858 in an 8-bit parallel or serial format. In fact, the AD9858 can operate at frequencies up to 2GHz because it includes a divide-by-2 circuit on the clock input port.

Sciteq Electronics, one of the pioneers of DDS technology, is now part of Meret Optical Systems. Meret Optics still supports many of Sciteq’s DDS products, including the gallium-germanium-based ADS-63x with clock frequencies up to 500 MHz. The module measures 5 x 7 x 1.125 inches and can be internally clocked or driven by an external clock. With its 32-bit frequency word and high bandwidth of 230 MHz, the DDS has a frequency resolution of better than 0.12 Hz and a frequency switching speed of better than 65 ns. Phase noise at a 1 kHz offset from a 100 MHz carrier is better than –105 dBc/Hz, and spurious levels at 180 MHz are less than –55 dBc.

In addition to PLL synthesizers and PLL/DDS combination devices, the company also offers the DCP-1 DDS module, which uses a dual accumulator architecture to generate linear frequency modulated waves (linear FM or chirp). The module runs at frequencies up to 500MHz and can generate output signals up to 230MHz in a 1×5×7-inch package. This compact module includes power supplies, reference sources, clock generators, output filters, control interfaces, and cooling fans for applications such as electronic warfare (EW), missile seekers, compressive receivers, and synthetic aperture radars (SAR). In addition, the company also offers rack-mount products with a housing height of 5.25 inches.

The WaveCor series of modular frequency synthesizers provided by ITT Microwave are also products based on DDS technology. Compared with Meret Optical, ITT Microwave obtained DDS technology from Stanford Telecommunications. ITT's STEL-2375B is a DDS chirp synthesizer with a maximum clock frequency of 1GHz and an output frequency range from DC to 400 MHz. Its 32-bit frequency resolution also makes the frequency step as fine as 0.23Hz, and its high-precision DAC has a spurious level of less than –50 dBc. The size of this modular synthesizer is only 2.33×1.14×0.21 inches.

The FSW190410-100 surface-mount unit from Synergy Microwave Corp. operates from 1900 MHz to 4100 MHz in 1-MHz steps and is one of the smallest frequency synthesizers in a package measuring just 0.940 × 0.940 × 0.300 in. The tiny synthesizer, which has an output power of +3 dBm and a spurious level of –70 dBc, settles to a new frequency in less than 10 ms (typical). Phase noise is –85 dBc/Hz and –110 dBc/Hz at 1 kHz and 100 kHz offsets from the carrier, respectively.

The FSS series of wideband modular frequency synthesizers from dBm covers the frequency range of 6 to 18 GHz. This compact unit has an output power of +13 dBm, a standard frequency resolution of 1 MHz, and a spurious content of –50 dBc. The phase noise at 100 Hz and 100 kHz offset from the carrier is –65 dBc/Hz and –90 dBc/Hz, respectively. This modular synthesizer measures 8.75 × 4.76 × 4.75 inches and uses a 14-bit binary control code with a switching time of no more than 200 ?s.

While many of the products mentioned above use DDS technology to achieve high resolution and high switching speeds, direct analog technology has been used for a long time to produce clean and stable output signals with extremely high switching speeds. One of the most well-known suppliers of such synthesizers, Aeroflex, offers the FS5000 direct analog frequency synthesizer for a variety of applications such as automatic test equipment (ATE), electronic warfare (EW) simulators, radar and radar cross-section (RCS) measurement. These synthesizers, which cover a frequency range from 300MHz to 26.5GHz, generate a set of frequencies by multiplying and dividing a reference source and select the desired output from it through switches and filters. Since all output frequencies are always "on", only selection is required to obtain the desired signal, so adjustment time is very short. Although this method uses a large number of components, it can achieve relatively high spectral purity (depending on the quality of the reference source) and the fastest switching speed.

For example, within the frequency range of this product, the FS5000 has a frequency switching time of 200ns or even shorter, an output power of +10dBm, and frequency switching is achieved through parallel BCD or GPIB control. This synthesizer uses a rack-mounted chassis, has a standard frequency resolution of 1MHz, and provides higher optional resolutions.

Herley-CTI's DS series of broadband direct frequency synthesizers cover a range of 10MHz to 20.48GHz, with frequency switching times of 30ns to 1?s, a frequency resolution of 1Hz, and a phase noise of –120 dBc/Hz at a 10kHz offset from a 10GHz carrier. For applications requiring smaller bandwidths, the company also offers the DSX series of direct frequency synthesizers, which cover a frequency range of 25% from 0.5 to 18.0 GHz.

The company also offers the VSS series of miniature frequency synthesizers for military and commercial applications. These compact synthesizers have a frequency range of 500MHz to 14GHz within 5%-17%, with phase noise of –115dBc/Hz and –137dBc/Hz at 10kHz and 100kHz offset from a 900MHz carrier, respectively. The product measures only 2.25×2.64×0.5 inches.

MITEQ's SLS series fast-tuning synthesizers have a tuning range of one-half octave from 1 to 15 GHz. This PLL-based synthesizer takes only 500 s to phase lock to a new frequency and has an in-band spurious performance of –70 dBc. The frequency step range is 200 kHz to 10 MHz (frequency dependent), and the minimum output power is +10 dBm.

Although Micro Lambda Wireless is best known for its low-noise YIG oscillators, it also offers frequency synthesizers based on YIG technology. For example, the MLSE series of broadband synthesizers has three models covering 2 to 20 GHz, 1 to 22 GHz, and 2 to 22 GHz, with a frequency resolution of 1 Hz. These products have an output power of up to +20 dBm, a switching time of 31 ms or less for full-bandwidth, and a switching time of 10 ms for hopping 100 MHz bandwidth. The spurious content is -60 dBc, while the phase noise at 100 Hz and 100 kHz offset from the 10 GHz carrier is –78 dBc/Hz and –117 dBc/Hz, respectively. The size of the MLSE synthesizer is 7 × 5 × 2.

The company has also developed the MLSL series of miniature frequency synthesizers based on permanent magnet YIG tuned oscillators (PMYTOs). The MLSL series has a frequency range of 2 to 12 GHz, a tuning step of 2 GHz, and a package size of 2.5 × 2.5 × 1.0 inches. The phase noise at a 10 kHz offset from the carrier is typically –98 dBc/Hz, and the spurious level is as low as -70 dBc. The series of synthesizers consumes less than 6 W and has a switching speed of 100 ms.

Wide Band Systems, perhaps best known for its instantaneous frequency measurement (IFM) receivers and digital frequency discriminators (DFDs), also offers a wideband, fast-tuning synthesizer that operates from 2.25 to 18.0 GHz. Available in a dual-rack-mount chassis or compact 6-by-6-by-1-inch modules, the synthesizer has an output power of +13 dBm and a maximum spurious level of –60 dBc. Phase noise at 1-kHz and 100-kHz offsets from the carrier is typically –75 dBc/Hz and –95 dBc/Hz, respectively. Switching speed is typically 3 s. Standard frequency resolution is 1 MHz, but products with resolutions up to 5 kHz are available.

Anritsu's MG3690B series of indirect frequency synthesizers are among the most powerful synthesizers, with standard models offering +17dBm output power (up to 20GHz) and non-standard products offering +23dBm output power (up to 20GHz). These synthesizers are available in a variety of bandwidths from 0.1Hz to 65GHz, and can jump 1GHz in about 5ms. If combined with the company's 63850-xx series of band-limited waveguide multipliers, the frequency range can be extended to 325GHz.

The UFS-18 direct analog synthesizer produced by Elcom Technology is also an ultra-wideband frequency synthesizer with a switching speed of 200ns and a frequency range of 300MHz to 1.8GHz. Its standard frequency resolution is 1Hz, the output power is +10dBm, and the spurious level is –65dBc. The phase noise at 10Hz, 100Hz, 10kHz and 10MHz offset from the 10GHz carrier is –55dBc/Hz, –85dBc/Hz, –117dBc/Hz and –140dBc/Hz respectively. The synthesizer has a built-in oven-controlled crystal oscillator (OCXO) with a frequency accuracy of 1PPM. The product can be remotely programmed via 44-bit parallel BCD command code or GPIB command code.

Figure 1: The PXI-5670 is a PXI vector signal generator with a frequency range of 250kHz-2.7GHz and a real-time bandwidth of 22MHz.

PTS (Programmed Test Sources) is one of the oldest suppliers of direct analog frequency synthesizers. Its highest-frequency instrument, the PTS 6400, can be adjusted from 1 Hz to 6400 MHz with switching times of 20 s or less. Although its basic architecture is analog, it also includes a DDS for phase-continuous switching, with a maximum frequency resolution of 1 Hz. Output power ranges from –3 to +7 dBm with ±1 dB flatness. The PTS6400 has phase noise of –99 dBc/Hz and –116 dBc/Hz at 100 Hz and 10 kHz offset from the carrier, respectively, and a noise floor of –136 dBc/Hz. Like the FS5000, it can be remotely programmed via BDC or GPIB.

FS5000 and PTS 6400 are representatives of full-size rack-mounted instruments. However, some users, especially those targeting military testing, want products with similar performance but more compact. To meet this demand, Aeroflex has developed the 3020 series PXI synthetic signal generator that occupies 3 slots in a 3U PXI chassis. The 3020 series includes three models with frequency ranges of 250MHz-2.5GHz, 250MHz-2.7GHz and 86MHz-6GHz, and a typical frequency switching speed of 250?s. The modulation bandwidth of this product is up to 28MHz, which can support complex modulation formats used in digital RF. The output power range is –120 to +5dBm, and the flatness is up to ±0.3 dB.

NI's PXI-5670 is another PXI synthetic signal generator that can generate vector output signals from 250kHz to 2.7GHz with a real-time bandwidth of 22MHz. It can generate 16-bit digital waveforms, so this three-slot, 3U PXI signal source (Figure 1) is very suitable for generating various modulation waves from quadrature amplitude modulation (QAM) to frequency shift keying (FSK) modulation. Its power output range is -145 to +13dBm, and the power adjustment speed is 35ms (typical value). The phase noise is typically -87dBc/Hz when offset 1kHz from the carrier, and the spurious level is typically -80dBc.

Figure 2: VMESG frequency synthesizer in VME module format, operating in the 0.5-18 GHz range.

To meet the stringent and changing requirements of military applications, Elcom Technology has developed the VMESG frequency synthesizer in a VME module format. The frequency synthesizer (Figure 2) occupies 3 or 4 slots in a VME host and uses a VME 64X interface to communicate with the host processor and other connected VME devices. Its frequency adjustment range is 0.5 to 18.0 GHz, with a frequency resolution of 1 Hz. The phase noise at 100 Hz and 10 kHz offset from the 10 GHz carrier is –75 dBc/Hz and –95 dBc/Hz, respectively. The phase noise at 10 MHz offset from the carrier drops to –1450 dBc/Hz. The harmonic level is –55 dBc, and the spurious level is as high as -60 dBc.

The VMESG frequency synthesizer provides +11dBm output power over a wide frequency range with an amplitude flatness of ±1dB. What sets this signal generator apart from other VME units is its frequency agility, with the ability to settle to 1dB in 200?s or less. The synthesizer can settle to a new amplitude level (within 1dB) in 50?s, and switching speed can be remotely controlled by sending commands on the 44-bit parallel BCD VME standard bus. As an alternative, the company also offers versions with GPIB or Ethernet interfaces.

Since some synthesizers need to generate digital modulation formats, they have external in-phase or quadrature (I/Q) modulation signal inputs or internal I/Q signal sources that can generate wideband modulation. Among these products, the 2910 series vector signal generator produced by Keithley Instruments is the latest one. The modulation bandwidth of this generator is 40MHz in the continuous frequency range of 400MHz-2.5GHz, and the modulation bandwidth can reach more than 100MHz if an external I or Q signal source is used. This half-rack instrument has a built-in arbitrary waveform generator and waveform library, and its application object is high-frequency testing that requires complex debugging formats.

The SMU200A vector signal generator (Figure 3) from Rohde & Schwarz offers even greater modulation bandwidth, with an I/Q modulation bandwidth of 200 MHz from 100 kHz to 2.2 or 3.0 GHz. This synthesizer has a phase noise of –135 dBc/Hz at 20 kHz offset from a 1-GHz carrier and, like the 2910, has a built-in arbitrary waveform generator.

In arbitrary waveform generators that define output waveforms through digital input signals, frequency synthesis technology and digital signal processing technology are increasingly integrated. Agilent's N8241A dual-channel synthetic instrument (SI) module is one of them. N8241A is designed to meet the needs of military testing for software-defined instruments. This product adopts the LXI (LAN eXtension for Instrumentation) module format, with a resolution of 15 bits and a maximum sampling frequency of 1.25GSps. It can generate single-ended or differential output signals with a bandwidth of 500MHz per channel or a bandwidth of 1GHz in I/Q format. The phase noise at 1kHz and 10kHz offset from the carrier is –95 dBc/Hz and –115 dBc/Hz respectively. The clutter performance is –75 dBc/Hz.

Figure 3: The SMU200A vector signal generator operates from 100kHz to 2.2 or 3.0GHz with an I/Q modulation bandwidth of 200MHz.

Although LeCroy mainly produces high-performance oscilloscopes, it also produces the PXA125 arbitrary waveform generator in a single-slot 3U PXI format. This signal source with a resolution of 14 bits and a maximum clock rate of 125MSps can modulate high-frequency carriers in various frequency forms from a microwave source. According to the 40% rule, it can generate an output signal of approximately 50MHz with a resolution of 1?Hz.

Tektronix also offers a series of arbitrary waveform generators with a sampling rate of 4.2GSps and a vertical resolution of 16 bits. The maximum sampling rate of its AWG710B is 4.2GSps and the maximum output frequency is 2.1GHz. This product has a real-time sequencer that can generate infinite waveform loops, frequency hopping modes and arbitrary IF and I/Q signals.