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A Pulse generator usually allows control of the pulse repetition rate, pulse width, pulse delay and pulse amplitude. More sophisticated pulse generators may allow control over the rise time and fall time of the pulses. A pulse generator’s delay is measured with respect to an internal or external trigger. The pulse generator’s rate may be determined by a frequency or period adjust (rep rate).
Pulse generators may use digital techniques, analog techniques, or a combination of both techniques to form the output pulses. For example, the pulse repetition rate and duration may be digitally controlled but the pulse amplitude and rise and fall times may be determined by analog circuitry in the output stage of the pulse generator. With correct adjustment, a pulse generator can also produce a 50% duty cycle square wave. Pulse generators are generally single-channel providing one frequency, delay, width and output. To produce multiple pulses, these simple pulse generators would have to be ganged in series or in parallel.
Some Pulse Generators like the BNC Model DB-2 Random pulse generator simulate actual operating conditions without requiring a live source and detector combination. Such parameters as frequency response, linearity, and discrimination levels may easily be measured without the inconvenience of dim oscilloscope display or long accumulation times by a pulse generator. Proper operation of baseline restorer circuits may be quickly verified. Scalers and ratemeters may be checked for satisfactory pulse recognition under random pulse (each pulse generator may be equipped with different capabilities and features).
The negligible amplitude shift with frequency of the pulser (pulse generator) makes the standard frequency test using a live source and a low rate precision pulse generator unnecessary.
Although most test applications will find the pulser connected to the test input of a charge sensitive preamplifier, it is possible to simulate the preamp itself with the pulse generator. The pulser is connected directly to the main amplifier and the preamp decay time constant is matched by proper selection of the pulser fall time. Set up of a system containing an inaccessible preamp can then be accomplished with ease.
For accurate simulation of detector pulse shapes, the rise time control should be adjusted to match 2.2 times the detector decay time constant. For example, if a pulse shape analyzer working with CsI-NaI phoswich is to be tested, the pulse generator rise time should be set to 0.5 µsec rise time for the NaI signal, and 2 µsec for the CsI signal. Intermediate signals are best obtained by mixing the outputs from two synchronized generators, 2 µsec rise time. By varying the amplitude ratio of the two generators, intermediate values of rise time are generated.
Solid state and plastic detectors have decay constants far shorter than the adjustment range of this generator. However, the shaping time constants used in virtually all systems are greater than the 100 nsec minimum rise time. The ballistic deficit formula predicts the reduction in amplitude, B. D., for a shaping system containing identical time constants for all shaping.
The external reference allows remote programming of the amplitude of the pulser, and the external trigger permits control of the output pulse rate. The latter provision is especially convenient if the average random rate needs to be controlled and an external random clock is unavailable. By placing the pulser in the random mode, a periodic waveform at the external trigger input will control the average random rate.
A new family of pulse generators can produce multiple-channels of independent widths and delays and independent outputs and polarities. Often called digital delay/pulse generators, the newest designs even offer differing repetition rates with each channel, differing delays and differing widths. They can be producing timing signals and operate in output modes independent of the other channels. These digital delay/pulse generator are useful in synchronizing, delaying, gating and triggering multiple devices usually with respect to one event. One is also able to multiplex the timing of several channels onto one channel in order to trigger or gate the same device multiple times.
These pulses can then be injected into a device under test and used as a stimulus or clock signal, or analyzed as they progress through the device, confirming the proper operation of the device or pinpointing a fault in the device. Pulse generators are also used to drive devices such as switches, lasers and optical components, modulators, intensifiers and resistive loads. The output of a pulse generator may also be used as the modulation signal for a signal generator.
Pulse Generator Multiplexing
A common request among Pulse Generator users is the ability to sum outputs on a single channel to create a more diverse pulse train. The BNC Model 575 Pulse Generator successfully achieves this function with the MUX feature described below.
Using the Output Multiplexer
Multiplexing allows for the combination of any or all channel settings to be output to any of the outputs. Channel multiplexing only combines timing events of the channels and not the actual output voltages or currents.
BNC Pulse Generators Summary:
Model 505 offers an Order of Magnitude Improvement: Digital Delay Pulse Generator
Berkeley Nucleonics Corporation (San Rafael, CA) has made an upgrade in the timing circuitry on the cost-saving Model 505 Pulse Generator. This Model 505 pulse generator is now shipping standard from the factory with 10nS delay and width resolution. This model represents an excellent value for users who need multiple channels of timing to gate, delay, synchronize or pulse various components to a research experiment. The 10nS edge resolution is available on all 16 edges (8 Channel Model).
“Delay and Width control on all 8 channels with 10nS resolution gives users the ability to address a handful of devices using a single Pulse / Delay Generator ,”comments Steve Cale, Senior Account Manager. “This is an excellent value for researchers working in the nanosecond and microsecond time domain when faced with declining budgets. I expect an increase in demand from federal R&D programs and university users.”
Berkeley states that they are improving the resolution of its Model 505 Pulse / Digital Delay Generator by an order of magnitude while keeping the same low price. The Model 505 gives users up to eight fully-defined pulse channels with 10nS resolutions for both delay and width. Gate widths are also achievable as narrow as 10nS. The product ships from stock, includes RS-232 and GPIB, and is priced at $1,990 for 2 Channels of Delay + Width, $2,496 for 4 Channels of Delay + Width, and $4,098 for 8 Channels of Delay + Width.
Model 725 Multi-Trigger Digital Delay Pulse Generator: The Model 725 addresses researcher’s and system integrator’s needs for extremely complex timing sequences. These timing requirements range from controls and diagnostics to signal quality monitoring and data acquisition. A wide range of signal filters, timing pulses, digital delay generation and cabling links can be accomplished with the Model 725. With its logic and timing capabilities, this is akin to a PLC (programmable logic controller) with precise timing.
The Model 725 coordinates, integrates and synchronizes complicated setups, simply, reliably and affordably. It features eight timing channels with programmable logic, unique timing modes and 10 ns edge resolution. Up to 8 Trigger Inputs can be logic signals, switches, transducers, interlocks, sensors, computer commands and gauges. The Model 725 can be programmed and controlled easily via Labview or Windows. It contains sophisticated logic, gating and filtering which enable up to eight channels/instrument with independent inputs, outputs and clocks/timers.
Model 575 Digital Delay Pulse Generator: 250pS Delay & Width resolution, and 200pS internal channel to channel jitter, make this a top performing pulse/delay generator. Up to 8 channels of delay and width.
Model 507 High Current Pulse Generator: This unique instrument provides a TTL Sync output to T0 along with high current, adjustable pulses. This is particularly useful as a reference source or trigger for cameras or other equipment in the user setup.
Model 6040 Pulse Generator: A modules electro/optical pulse generator, this unit offers adjustable rates up to 100 MHz, electrical signals to 800V amplitudes, optical pulses at 650nm, 904nm, 1064nm, 1310nm nd 1550nm, and 1 ns resolution delay and width control.
Model PB-5: Our latest in NIM Programmable Pulsers, the Model PB-5 replaces the BH-1, DB-2, BL-2, 9010, GL-3 and LG-1. Along with a suite of features and modes, the PB-5 is widely respected for its 155 uV amplitude resolution