B&K 4070A user manual Introduction to the Arbitrary Waveform System

7.2 Introduction to the Arbitrary Waveform System

7.2.1 Description of the Arbitrary Waveform Generator

The Arbitrary Mode lets the user design custom waveforms on a PC and download them to the 4070A for generation including Arbitrary Waveform system is a fully featured Function Generator. Function generator offers a set of pre -stored waveforms. Signals are generated using the Arbitrary Waveform hardware. User may select from many stored waveforms, and may also specify a repetition rate to 2 MHz. All functions could be generating on a continuous or triggered basis. High-going pulse is given on the SYNC Out connector at the start of each waveform.

Also included with the Arbitrary Waveform system is a variable duty cycle Pulse Generator. Pulse Generator allows the user to generate pulse waveforms with varying amplitude, offset, frequency and duty cycle

Introduction

Output signal form is generated by sending values to a Digital to Analog converter (DAC) from a ram memory. High-speed counter generates sequential addresses which indexes successive ram values for the DAC, clock for the counter is derived from the same DDS system used to generate the DC-21.5 MHz output of the 4070A. Because the Arbitrary waveform system uses the fully synthesized DDS system for its clock, the arbitrary waveform generator has a highly accurate and stable clock source adjustable from DC to 40 MHz in .01 Hz steps.

	DDS	DC-20 MHz		Freq.
	Clock			Doubler
	Generator
DC-40 MHz clock
Counts 0,1,...N,0,1,...
		15			13
			32K x 16
	Counter
		Addr	RAM		Data

	9th Order Bessel
		Fc = 10 MHz
12 Bit		Low Pass
DAC		Filter

Extra Data bit

TTL/CMOS

Buffer

Gain	SIG Out
Control	(Front Panel)

SYNC Out

(Front Panel)

Figure 7.2.1-1: Arbitrary Waveform Generator block diagram

Logic level output is provided on the SYNC Out connector. This output signal could be used to assert a digital pulse on any data point, with is useful to generate synchronous pulses with the analog data or to generate arbitrary digital waveforms.

The 4070A receives arbitrary waveform data through the serial port on the rear of the 4070A. An incoming waveform is stored in successive ram locations beginning at address 0. After the last data point is received, the system processor adds a special “end of data” bit to the last data point, instructing the counter hardware to reset to the waveform start address after the last data point is sent to the DAC. Waveforms may be conveniently saved to nonvolatile memory.

Those waveform values could be sent to the 4070A in a variety of formats. ASCII formats include floating point, time & value floating point, decimal, hexadecimal, and integer. Binary format is also supported.

Waveforms may be generated in Continuous or Triggered modes. In continuous mode, the waveform is immediately restarted after the last point in the waveform is generated. In Triggered mode, the waveform halts after the last data point has been generated. The system then awaits another Trigger condition before generating the waveform again.

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BK Precision 4070A User Manual Rev.2.2