Information About Analog signal generators

Analog signal generators

Analog Signal Generators are capable of producing CW (continuous wave) tones. The output frequency can be tuned anywhere over their entire frequency range. In addition, many models offer various types of analog modulation, either as standard equipment or as an optional capability to the base unit. This could include AM, FM, ΦM (phase modulation) and pulse modulation. Another common feature is a built-in attenuator which makes it possible to vary the signal’s output power. Depending on the manufacturer and model, output powers can range from -135 to +30 dBm. A wide range of output power is desirable, since different applications require different amounts of signal power. For example, if a signal has to travel through a very long cable out to an antenna, a high output signal may be needed to overcome the losses through the cable and still have sufficient power at the antenna. But when testing receiver sensitivity, a low signal level is required to see how the receiver behaves under low signal-to-noise conditions. Analog signal generators have been available for decades from various manufacturers. One of the earliest implementations was the HP200A Audio Oscillator, the first product sold by the Hewlett-Packard Company in 1939.

Vector signal generators

With the advent of digital communications systems, it is no longer possible to adequately test these systems with traditional analog signal generators. This has led to the development of vector signal generators, also known as digital signal generators. These signal generators are capable of generating digitally-modulated radio signals that may use any of a large number of digital modulation formats such as QAM, QPSK, FSK, BPSK, and OFDM. In addition, since modern commercial digital communication systems are almost all based on well-defined industry standards, many vector signal generators can generate signals based on these standards. Examples include GSM, W-CDMA (UMTS), CDMA2000, LTE, Wi-Fi (IEEE 802.11), and WiMAX (IEEE 802.16). In contrast, military communication systems such as JTRS, which place a great deal of importance on robustness and information security, typically use very proprietary methods. To test these types of communication systems, users will often create their own custom waveforms and download them into the vector signal generator to create the desired test signal.

Logic signal generators

Also known as 'data pattern generator' or more often 'digital pattern generator', this type of signal generators produces logic types of signals - that is logic 1's and 0's in the form of conventional voltage levels. The usual voltage standards are: LVTTL, LVCMOS. As such, they must be distinguished from 'pulse/pattern generators', which refers to signal generators able to generate logic pulses with different analog characteristics (such as pulse rise/fall time, high level length, ...). Logic signal generators (digital pattern generators) are used as stimulus source for digital integrated circuits and embedded systems - for functional validation and testing.

20th Jan 2015

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