News and New Products

2G sample/sec waveform generators resolve 14 bits vertically, 12 digits in frequency

By Dan Strassberg, Contributing Technical Editor -- EDN, 8/23/2005

Six new arbitrary-function generators from Tektronix, the AFG3000 series, generate sine, square, pulse, arbitrary, ramp, sin(x)/x, Gaussian, Lorenz, exponential rise/decay, haversine, and noise waveforms as well as dc voltages. The 9.9-lb units sell for $1780 to $8500 and are available in 6.2×13×6.6-in. cases approximately the size of the company’s top-selling TDS3000-series digital scopes. Three of the units produce single-channel outputs, and three produce two-channel outputs. The lowest priced family members create sine waves with frequencies to 25 MHz, square waves, pulses, and arbitrary waveforms to 12.5 MHz, and other waveforms to 250 kHz. For the midpriced units, the three frequency ranges extend to 100, 50, and 1 MHz, and, for the top-of-the-line units, the ranges extend to 240, 120, and 2.4 MHz. For all six units, the lowest output frequency for all three waveform classes is 10^–3 Hz; the frequency resolution is 1 µHz, or 12 digits; timebase stability is ±1 ppm/year; vertical resolution is 14 bits; and amplitude resolution is 0.1 mV p-p, or four digits.

The arbitrary-waveform memory of the lowest priced units is 1k to 64k samples, and the maximum rate at which the units convert digital values to analog is 250M samples/sec. The same sample rate applies to the midpriced and top-of-line units when waveform data sets comprise 16k to 128k samples. For data sets of 16k samples or fewer, the midpriced units can convert at 1G sample/sec. For data sets of the same size, the top-of-line units can convert at 2G samples/sec.

All units can perform amplitude-, frequency-, phase-, and pulse-width modulation and frequency-shift keying, as well as linear and logarithmic sweeps. The low-priced and midpriced units deliver 10V p-p into 50Ω, whereas the wider bandwidth, top-of-line units deliver 5V p-p into 50Ω. The two lowest priced units include front and rear USB ports for attachment of a memory-stick device and connection to a host PC, respectively. To the USB ports, the midpriced and top-of-line units add LAN and IEEE 488 connections. AFG3000 generators’ proprietary waveform format is compatible with Tektronix’s free ArbExpress 2.0 waveform creation and editing software. ArbExpress, which is also compatible with most Tek oscilloscopes and with The MathWorks (www.mathworks.com) MatLab, also supports CSV (comma-separate value) format for compatibility with many other applications including Excel (www.microsoft.com).

All of the generators sport 5.6-in. LCDs, which, except for that of the lowest priced unit, produce color displays. The displays provide information in both numeric and graphical forms. Although the graphical displays resemble those of oscilloscopes, Tek point outs that the generators are not scopes. For example, if you set the generator to produce a sine-wave carrier at, say, 500 kHz, with amplitude modulated by another sine wave at, say, 1 kHz, you might expect to see the carrier sine waves scrunched-up and displayed as a bright band whose amplitude the modulating audio-frequency sine wave determines. Instead, the generator represents the carrier frequency by a much lower frequency, so you can see the carrier-frequency waves’ sinusoidal shape. On the generator’s screen, only 13 carrier-frequency sine waves appear in two cycles of the modulation—a far cry from the 1000 cycles in the waveform the generator produces.