7D20

The Tektronix 7D20 is a two-channel digitizing plug-in for 7000-series scopes. It is a triple-width plug-in and provides both vertical and horizontal signals to the scope. The 7D20 can digitally store waveforms and has a GPIB interface.

Manuals – Specifications – Links – Pictures

A special version of the rackmount large screen R7603 exists (Opt. 20), which provides a rear-panel GPIB connector to be used with the 7D20.

Key Specifications

Bandwidth	0–70 MHz (DC), 10 Hz–70 MHz (AC)
Rise time	< 5 ns
Sampling Rate	40 MSps
Resolution	8 bit
Deflection	5 mV/Div to 5 V/Div (1–2–5)
Input impedance	1 MΩ // 20 pF
Time base	50 ns/Div — 1 μs/Div: Equivalent Time Mode 2 μs/Div — 200 μs/Div: Extended Real Time Mode 500 μs/Div — 50 ms/Div: Real Time Mode 100 ms/Div — 20 s/Div and External: Roll Mode
External clock	< 10 kHz
Memory	2 × 455 cells (alternating) analog / 1024 words digital
Features	2 channels 6 memory banks 2 cursors
Weight	3.9 kg (8.5 lb)

Internals

The 7D20 uses an analog shift register (CCD) for high-speed signal acquisition, and then digitizes the stored analog signal at a lower speed (see Patent US 4527117A). This design allowed the 7D20 to capture single-shot events at 40 MSamples/s even though this exceeded the speed of ADCs of the time. A microprocessor (68B09) in the plug-in controls most of its functions.

The analog waveforms that are sent to the 7000-series mainframe are generated by vertical and horizontal DACs. The DACs outputs can be calibrated for scaling and shift so that signals are accurately displayed on the oscilloscope screen.

The 7D20 has a "roll" mode that emulates a paper roll chart, as if the waveform were being drawn by a pen on the right side of the screen while the paper is being moved to the left at a constant rate. No equivalent to "roll" exists in analog scopes. The Tektronix 2212/2216, 2220/2221/2230 and possibly others also have this feature.

The 7D20 can give NVRAM errors that are often easy to fix.

Links

• 7D20 page @ amplifier.cd
• EB5AGV's Tektronix R7603 / 7D20 page - 7D20+R7603 Repair Report
• Another 7D20 repair
• 7D20 @ barrytech.com

Pictures

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  7D20 picture from manual

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  7D20 picture in 7603 mainframe, from manual

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Parts