FUNCTION GENERATORA function generator is usually a piece of electronic test equipment or software used to generate different types of electrical waveforms over a wide range of frequencies. Some of the most common waveforms produced by the function generator are the sine, square, triangular and saw-tooth shapes.
FUNCTION GENERATORThe waveforms generated by a function generator can be either repetitive or single-shot (which requires an internal or external trigger source). Integrated circuits used to generate waveforms may also be described as function generator ICs.
FUNCTION GENERATOROther important features of the function generator are continuous tuning over wide bands with max-min frequency ratios of 10:1 or more, a wide range of frequencies from a few Hz to a few MHz, a flat output amplitude and modulation capabilities like frequency sweeping, frequency modulation and amplitude modulation.
FUNCTION GENERATORFunction generators are used in the development, test and repair of electronic equipment. For example, they may be used as a signal source to test amplifiers or to introduce an error signal into a control loop.
FUNCTION GENERATORAlthough function generators cover both audio and RF frequencies, they are usually not suitable for applications that need low distortion or stable frequency signals. When those traits are required, other signal generators would be more appropriate.
FUNCTION GENERATORA typical function generator can provide frequencies up to 20 MHz. RF generators for higher frequencies are not function generators in the strict sense since they typically produce pure or modulated sine signals only.
FUNCTION GENERATORMore advanced function generators are called arbitrary waveform generators (AWG). They use direct digital synthesis (DDS) techniques to generate any waveform that can be described by a table of amplitudes.
FREQUENCY SYNTHESIZERA frequency synthesizer is an electronic system for generating any of a range of frequencies from a single fixed time-base or oscillator. They are found in many modern devices, including radio receivers, mobile telephones, radiotelephones, walkie-talkies, CB radios, satellite receivers, GPS systems, etc.
FREQUENCY SYNTHESIZERA frequency synthesizer can combine frequency multiplication, frequency division, and frequency mixing (the frequency mixing process generates sum and difference frequencies) operations to produce the desired output signal.
FREQUENCY SYNTHESIZERThree types of synthesizer can be distinguished. The first and second type are routinely found as stand- alone architecture: Direct Analog Synthesis (also called a mix-filter-divide architecture) and by comparison the more modern Direct Digital Synthesizer (DDS). The third type are routinely used as communication system IC building-blocks: indirect digital (PLL) synthesizers including integer-N and fractional-N.
FREQUENCY SYNTHESIZERPrior to widespread use of synthesizers, radio and television receivers relied on manual tuning of a local oscillator.Variations in temperature and aging of components caused frequency drift. Automatic frequency control (AFC) solves some of the drift problem, but manual retuning was often necessary.
FREQUENCY SYNTHESIZERSince transmitter frequencies are well known and very stable, an accurate means of generating fixed, stable frequencies would solve the problem.Many coherent and incoherent techniques have been devised over the years. Some approaches include phase locked loops, double mix, triple mix, harmonic, double mix divide, and direct digital synthesis (DDS).
FREQUENCY SYNTHESIZERThe vast majority of synthesizers in commercial applications use coherent techniques due to simplicity and low cost.Synthesizers used in commercial radio receivers are largely based on phase-locked loops or PLLs. Many types of frequency synthesizer are available as integrated circuits, reducing cost and size.
FREQUENCY SYNTHESIZERThe trial and error method was once the work-horse for designers of frequency synthesizers.This began to change with the works of Floyd M. Gardner (his 1966 Phaselock techniques) and Venceslav F. Kroupa (his 1973 Frequency Synthesis). Manassewitsch calls this the Brute-force approach. Techniques and formulae have been provided by Dean Banerjee.
FREQUENCY SYNTHESIZERVarious other mathematical techniques used in the frequency synthesizer are as follows: Gearbox approach: Analogous to the mechanical gear ratio relationship, the frequency synthesis factor is composed of multiplicative integers in the numerator and denominator.Modulo-N approach
FREQUENCY SYNTHESIZER The block diagram shows the basic elements and arrangement of a PLL based frequency synthesizer.
FREQUENCY SYNTHESIZERPractical considerations:In practice this type of frequency synthesizer cannot operate over a very wide range of frequencies, because the comparator will have a limited bandwidth and may suffer from aliasing problems. This would lead to false locking situations, or an inability to lock at all. In addition, it is hard to make a high frequency VCO that operates over a very wide range.
FREQUENCY SYNTHESIZERFurther practical aspects concern the amount of time the system can switch from channel to channel, time to lock when first switched on, and how much noise there is in the output. All of these are a function of the loop filter of the system, which is a low-pass filter placed between the output of the frequency comparator and the input of the VCO.
FREQUENCY SYNTHESIZERThus the design of the filter is critical to the performance of the system and in fact the main area that a designer will concentrate on when building a synthesizer system.
SFG 2000/ SFG 2100 SERIES SFG-2000 series uses the latest Direct Digital Synthesis (DDS) technology to generate stable, high resolution output frequency.In DDS, the waveform data is contained in and generated from a memory. A clock controls the counter which points to the data address. The memory output is converted into analog signal by a digital to analog converter (DAC) followed by a low pass filter.
SFG 2000/ SFG 2100 SERIESThe resolution is expressed as fs/2k where fs is the frequency and k is the control word, which contains more than 28bits. Because the frequency generation is referred to clock signal, this achieves much higher frequency stability and resolution than the traditional function generators.
SFG 2000/ SFG 2100 SERIESThe block diagram is as shown.
SFG 2000/ SFG 2100 SERIESDDS synthesizer consists of Phase accumulator (counter), lookout table data (ROM), Digital-to- analog converter (DAC), and Low-pass filter (LPF).The phase accumulator adds the frequency control word K at every clock cycle fs. The accumulator output points to a location in the Table ROM/RAM. The DAC converts the digital data into an analog waveform. The LPF filters out the clock frequency to provide a pure waveform.
SFG 2000/ SFG 2100 SERIESPerformance: • High resolution using DDS and FPGA technology • High frequency accuracy: 20ppm • Low distortion: −55dBc • High resolution 100mHz maintained at full range
SFG 2000/ SFG 2100 SERIESFeatures : • Wide output frequency range: 4, 7, 10, 20MHz • Various output waveforms: Sine, Square, and Triangle • TTL/CMOS output • Counter up to 150MHz high frequency (SFG-2100 series) • AM/FM with internal and external (SFG-2100 series)
DS335The DS335 is a simple, low-cost, 3 MHz function generator based on Direct Digital Synthesis (DDS) architecture.Basic functions include sine waves and square waves (up to 3.1 MHz), and ramps and triangles (up to 10 kHz).
DS335All functions can be swept logarithmically or linearly in a phase-continuous fashion over the entire frequency range. A rear-panel SWEEP output marks the beginning of a sweep to allow synchronization of external devices. Both unidirectional and bidirectional sweeps can be selected.
DS335Toggling is done either at a fixed, internal rate of up to 50 kHz, or externally via a rear-panel input. Outputs have the low phase noise inherent to DDS
DS335Wideband amplifiers maintain good pulse response and provide low distortion. The result is an output capable of driving 10 Vpp into a 50 Ω load, or 20 Vpp into a high-impedance load.
DS335Both GPIB and RS-232 interfaces are available to provide complete control via an external computer. All instrument functions can be set and read via the computer interfaces.
DS335GeneralInterfaces Optional RS-232 and GPIB. All instrument functions are controllable over the interfaces.Non-volatile memory Up to nine sets of instrument settings may be stored and recalled.Dimensions 8.5" × 3.5" × 13" (WHD)Weight 8 lbs.Power 22 W, 100/120/220/240 VAC, 50/60 Hz.
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