What is a PRBS Generator?
A pseudo random binary sequence (PRBS) generator is a common used piece of test equipment in electronics labs. The pseudo random data allows one to more thoroughly evaluate the behavior of the device under test (DUT) as opposed to using a predictable input test signal. ADSANTEC’s ASNT_PRBS45 is a great example of such a generator that can be used in numerous ways including test applications, design verification, and R&D efforts in general.
What do you need to run it?
To function correctly, all the unit needs besides power is a half rate input clock signal. For example, to produce its highest date rate output of 45Gb/s, the unit only requires a 22.5GHz input clock. The PRBS generator features one differential data output port, one differential half rate clock output port, and a single-ended divided down clock output to be used as an oscilloscope synchronous signal. The ASNT_PRBS45 can produce not only a PRBS output signal from 27-1 up to 231-1, but is word programmable as well making the unit in general a pattern generator.
ASNT_PRBS45 (PRBS Generator up to 45 Gbps)
A Good Idea:
While a high level of engineering has been applied to the generator’s output to produce as clean of an output data eye as possible, the quality of it still depends on the type and length of the cable the user decides to employee in his or her test setup. This random selection of cable makes it impossible to tune the PRBS generator’s output to the optimal setting since different cables introduce varying channel characteristics. To overcome this issue, an adjustable pre-emphasis amplifier can be used immediately following the PRBS generator. Now depending on the type and length of cabling used, the pre-emphasis amplifier can be dynamically tuned to eliminate the negative effects of them. In this way, the output data eye is optimized at the end of the attached cable before being inserted into the DUT.
Benefits of Adding the Pre-Emphasis Amplifier.
The ASNT6118-MOD is a 4-tap pre-emphasis driver that works up to 32Gb/s. By adjusting the polarity and weights of the individual taps, the user is able to overcome many of the signal degradation effects introduced by cabling that is utilized in test laboratory environments. The easy to use instrument requires only a clock and data input and is easy controlled using a user friendly GUI. A two times clock multiplier is included so input clock frequencies only up to 16GHz are needed. The unit also allows users to adjust the amplitude, crossing point, and peaking of the data output for further data eye optimization.
ASNT6118-MOD (Pre-Emphasis Amplifier / Driver)
Bonus Features of Pre-Emphasis:
A bonus feature of the ASNT6118-MOD is that with the correct settings of the taps, a pseudo PAM4 signal can be generated. With all 4 levels that can be adjusted, this signal provides a great way to evaluate PAM4 receivers or any other devices in this area.
Better Together:
A PRBS generator combined with a pre-emphasis amplifier is great way to generate high quality data signals for testing purposes. The adjustability of the pre-emphasis amplifier allows the user to generate wide open eye diagrams with low jitter at the end of most reasonable cabling commonly used in the high speed electronics labs.
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