Difference between revisions of "BNC 575"

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BNC 575 is electronic test equipment, which is the 2007/2008 version of a series of benchtop digital delay generator/pulse generator that began with the BNC 400 and BNC 500 in 2000. This version improves upon the earlier designs with better resolution (250ps), more channels (up to 8, each with separate delay and widths) and more functionality (summed channels, more output and input options, more allowable communication protocols.) Channel-to-channel and external trigger jitter have both been significantly improved from earlier designs. The BNC 575 replaces the BNC 565 and BNC 555. New capabilities include int/ext clock for synchronizing and pulse picking, summing timing of several channels onto one, independent trigger and gate and selectable timing reference for each channel.

The BNC 575 features a single timing board that is coupled to modular input boards and modular output boards. In this way the BNC 575 can be configured to have a number of different electrical and optical inputs and outputs. This designs also allows for customization of the unit. For example, optical outputs were developed to deliver timing pulses in a harsh electrical environment. The Gate input can be converted to a second Trigger input, and one can select which channel operates with which of the two triggers.

Personal Computer to Pulse Generator Communication-RS232, USB, Ethernet and GPIB The 575 comes standard with RS232 and USB; Ethernet and GPIB interfaces are optional. All menu settings can be set and retrieved over the computer interface using a simple command language. The command set is structured to be consistent with the Standard Commands for Programmable Instrumentation (SCPI). The syntax is the same for all interfaces.

Basic operation and quick start

There are several independent settings that one may access. These are Channel, Mode, Rate, Trig, Gate, System, Store and Recall.

Default settings allow you to quickly get an output. Turn the instrument on. Push Run/Stop (The Run/Stop button is a toggle operation and the blinking circle in the upper left corner indicates that the instrument is triggering or is enabled.) You should now be able to see a pulse on your scope from all of the channels. If at any time you get in trouble, you can recall the default settings from memory location 0.

The BNC 575 has both FUNCTION and CHANNEL buttons. The FUNCTION button accesses the function that is printed in yellow over the next button you push (e.g. Mode, Aux1, System). We will discuss the CHANNEL settings first because that is the display you see when you first turn the instrument on.

Channel settings

Each channel can have settings independent of the other channels. Each can have its own timing and its own amplitude settings. Channel A appears on the display after you turn the instrument on. Push Channel A’s button repeatedly to cycle through A’s properties. Go back to the original display.

The cursor blinks on the line that is currently active and changeable. To activate another line in the display, push the Select/Adjust spinner knob. Push the Select/Adjust knob to get to the Wid: line. Delay and Width settings – Each channel provides you with width and delay controls. To change the width of the pulse you must get the cursor to blink on the Wid: or Dly: line. Use cursor and arrows, cursor and spinner knob or numeric insertion to change the width or delay. Enabled/Disabled – You are able to disable the outputs of individual channels by selecting the disable mode. Note that when you Disable a channel the light in that channel’s pushbutton goes dark. Push Channel A’s button again. Pol: – This allows you to decide whether the pulse goes from low to high (Active High) or high to low (Active Low) during the Width. Out:– This allows you to decide whether the pulse amplitude is TTL/CMOS or Adjustable. If you select Adjustable, it allows you to select the Amplitude. Push Channel A’s button again. Mode: – This allows the Channel to operate in Normal, Single Shot, Burst or Duty Cycle modes. Incoming pulses are provided to all channels equally. The channels are able to process the incoming pulses according to their own channel’s Mode: setting. Normal – Produces one pulse for each incoming pulse. Single Shot – Produces just one pulse and stops until you reset. Burst – Produces a selectable number of pulses and stops until you reset. Duty Cycle – Lets you select the number of On pulses that occur and the number of Off pulses that must be ignored before On pulses occur again. This is a continuous operation. A typical application is to divide by N with 1 pulse On for every N-1 pulses Off. One may use one channel to repeatedly trigger flash lamps and use the divide by N feature to fire the Q-switch and another divide by N channel to delay and gate a detector with respect to the Q-switch. Push Channel A’s button again. Wait: Allows you to select the number of trigger pulses that a channel receives before outputting a pulse. If you just want one pulse after another channel outputs N pulses, set Wait: to N and set Mode: to Single Shot. Push Channel A’s button again. Ch: and Mux: NOTE: Beginning with firmware revision 2.1.3, Mux settings are in the Advanced Channel Menu

Push Function then Channel A button. This accesses the advanced channel menu. Sync Source: Allows you to select either To or another channel as the reference of zero delay for Channel A. Ch Gate: You select which of the channels are affected by the incoming Gate. The gate for this channel may be disabled or operated in Pulse Inhibit or Output Inhibit. The polarity and threshold for the Gate is also selected. (see description for Gate operation below.) Ch: and Mux: (Beginning with firmware revision 2.1.3) These settings allow you to multiplex the timing of selected channels onto this output. The channels that are selected to be multiplexed have a 1 under the channel letter. For example if you want to sum channels A and B onto channel A’s output, select 1’s under both A and B. In this mode, you can generate pulse trains of unequal spacings and durations.

FUNCTION Settings

The function button allows you to select a number of functions printed in yellow. One pushes first the yellow Function button and then another button to select Mode, Rate, Help, Aux1, Aux2, Aux3, System, Store, Recall and even a Channel button.

Push the Function button and then the Rate button. Per: - Period denotes the period of the continuous To pulses that can be selected to be your internal trigger. Source: Selects whether you use the internal system clock or an external clock of 10, 20, 25, 40, 50, 80 or 100 MHz that you supply. Push the Function button and then the Rate button again. Ref Out: You may select discrete values from 100 MHz to 10 MHz as well as To.

If you wish to synchronize several units to the same clock, select one you may use the Clock Out and Clock In rear panel connections. One unit is the master and one connects its 100 MHz clock out to the next unit, which in turn supplies the clock to the unit after it.


Push the Function button and then the Mode button. Mode - This function determines how triggers are presented to the channels. This is the master clock to all the channels. These triggers may be internally or externally-derived. Internally-derived clocks may be the continuous To whose Period you’ve set. It may also be a one and only one pulse, a burst or a series of On/Off pulses. Externally-derived triggers may be the aperiodic external triggers that one inserts at the Trig connector.

For digital delay operation, set the Mode to Single Shot to provide a single clock to the channels with each Ext Trig. For pulse generator operation, set the Mode to Continuous to get delays and widths at the To period. This continuous operation can be pushbutton or external trigger activated. Continuous – When you push Run/Stop, a stream of continuous pulses triggers the channels. To Stop the continuous stream, push Run/Stop again. You can Ext Trig a continuous stream by enabling the Trig and operating in continuous. Press Run/Stop to arm the Trig and insert a trigger pulse to start continuous operation. Single Shot – Provides only one trigger to the channels with each Ext Trig or each Run/Stop button depression. Burst – Provides just N triggers in a burst to the channels. These might originate from Ext Trig or Run/Stop at the To rate. Duty Cycle – Provides a number of OFF triggers and a number of ON triggers to the channels. These might follow the Ext Trig or the To rate.

Store and Recall – These buttons allow you to store and recall complete settings for all the channels and functions. You can give a name and number to the settings you are saving for future recall.

System – This sets programming properties for RS232, USB, GPIB and Ethernet. Interface: Selects the programming protocol and provides the appropriate setup for that protocol.

Aux1, Aux2, Aux3 – These button will be used for custom applications. Timing and outputs can be customized to meet the needs of system integrators and these buttons will facilitate those custom operations.

Trig settings – This sets properties of the external trigger circuit. One selects levels and triggering edges and whether the unit is to be triggered. Mode: Triggered activates the trigger. Disabled – the unit will not accept external triggers. Level: Sets the trigger threshold. Edge: Selection of rising or falling edge of the incoming pulse that the unit triggers on.

Gate settings - Selects the gate mode and level. Mode: Selects Output Inhibit, Pulse Inhibit, Disabled, Channel Menu. Output Inhibit shuts the output off immediately. Pulse Inhibit shuts the output after the current pulse has been completed. Gate may affect all the Channels as a system gate or may control each Channel independently. An Advanced Channel Menu selects the individual Channel(s) Gate input control. To access Advanced Channel Menu push Function then the Channel letter. The Gate signals have no effect when the Disabled mode is selected. Level: Selects the input threshold. Logic: Selects Active Low or Active High. Active High allows pulses to occur when the input level is above the threshold. Conversely, Active Low allows pulses to occur when the input level is below threshold.

References

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