155-0032-00

The Tektronix M55  (P/N 155-0032-00,155-0032-01) is a variable-gain transconductance amplifier (voltage in, current out) monolithic integrated circuit in a 16-pin DIP. The 155-0216-00 and 155-0217-00 (M55D aka M055D) appear to be improved successor versions.

Regarding the 155-0032-xx, John Addis says,

The 155-0032-00’s IC process had an FT of 1.0 GHz, rather inadequate for the job, but that was all there was at the time. The on-chip resistors were diffused (there were no thin film resistors in that process) and thus had too poor a temperature coefficient and tolerance for use as gain-setting resistors.

As you can see, there are two separate gain choices determined by which set of emitters is chosen, pins 1 and 16, or 2 and 15. This selection is made off chip by choosing Q205 or Q215 to carry the current through R212. Pot R217 allows DC balance at 5 mV/div to match that at all other sensitivities, controlled elsewhere.

Pin 12 ultimately selects which pair of the four output cross-connected transistors passes the signal current from the two transistors whose bases are connected to pin 4. Which pair of output transistors is chosen determines the polarity choice of the output signal (Normal or Invert). This same pair of transistors also enables variable gain by allowing a controlled amount of cross-coupling of the signal.

This is an undesirable way of doing variable gain control, but neither Roy nor I knew that at the time. It is a noisy configuration. At the 0% signal gain there is lots of noise gain. It has poor thermal balance at anything other than 100% and the not very useful 0% signal gain. In between 0% and 100% gain, the circuit is poor in noise and thermal balance.

I went on to use the same Gilbert multiplier circuit in the 155-0078-xx (M84) and made the same bad choice again in the 7A29. In our defense, with just two stages and the need to do both invert and variable gain control somewhere, there was not a lot of choice.

It was not until I designed the M377 for the 11000 series of plugins (11A32, 11A33, 11A34, 11A52) that I finally got it right. (See the British magazine Electronic Engineering, September, 1988, pp 40-41.)

The M377 was a single-channel plugin on a chip with 0 V common mode input and output voltages, very linear variable gain control, two four pole bandwidth limits, and three outputs which could be individually inverted and turned on or off.

The M377 was the first wideband analog IC with DC level shift on chip (allowing 0 V common mode input and output and without PNP transistors), the first wideband amplifier with any on-chip bandwidth limit selection, the first to have more than two fixed gain settings (it has six), the first to require only one transient response adjustment (no thermals), and the first to have a highly linear relationship between a control voltage and gain. It also had excellent overdrive recovery. Live and learn.

The input differential amplifier's emitters are brought out to pins 1 and 16. Off-chip components provide frequency compensation and determine the gain. The chip has an input to select normal or inverted phase and an input to vary the "position", i.e., output current offset.

• Pin 1: emitter current source
• Pin 2: gain switching
• Pin 3: input balance
• Pin 4: bias
• Pin 5: −8 V
• Pin 6: position current source
• Pin 7: ground
• Pin 8: signal out −
• Pin 9: signal out +
• Pin 10: position
• Pin 11: +8 V
• Pin 12: norm / -inv
• Pin 13: +5 V
• Pin 14: signal in −
• Pin 15: gain switching
• Pin 16: emitter current source

Used in

• The 155-0032-00 is used in the front end of the 335 signal path, just after a JFET high-impedance buffer. It is discussed on page 3-5 of the 335 manual.
• The 155-0032-00 is also used as the trigger amplifier in the 465. In this application, the input differential amplifier has a total tail current of about 11 mA.
• The 155-0032-00 is used as a vertical gain stage in the 7A12.
• 475 (U520, U720)
• FG504 (U770) below SN B057720
• 1440 (-01), 1460 (-01), 1478 (-01)
• 1480, 1481, 1482, 1485
• 464, 465, 465B, 466, 475, 475A, 475M
• 634, 650, 651, 652, 653, 655, 656, 670, 671
• See also 155-0217-00

Some instruments using part 155-0032-00

Instrument	Manufacturer	Class	Model	Description	Introduced
1440	Tektronix	Audio/Video	1440	Automatic Video Corrector	1974
1480	Tektronix	Audio/Video	1480	NTSC waveform monitor	1976
1481	Tektronix	Audio/Video	1481	PAL Waveform Monitor	1977
1482	Tektronix	Audio/Video	1482	PAL-M Waveform Monitor	(?)
1485	Tektronix	Audio/Video	1485	TV waveform monitor	(?)
335	Sony/Tektronix	Oscilloscope	335	Compact dual-trace 35 MHz oscilloscope	1976
464	Tektronix	Oscilloscope	464	Portable 100 MHz dual-trace storage scope	1975
465	Tektronix	Oscilloscope	465	Portable 100 MHz dual-trace scope	1972
465B	Tektronix	Oscilloscope	465B	Portable 100 MHz dual-trace scope	1980
466	Tektronix	Oscilloscope	466	Portable 100 MHz dual-trace storage scope	1974
475	Tektronix	Oscilloscope	475	Portable 200 MHz dual-trace scope	1972
475	Tektronix	Oscilloscope	475	Portable 200 MHz dual-trace scope	1972
475A	Tektronix	Oscilloscope	475A	Portable 250 MHz dual-trace scope	1977
634	Tektronix	Oscilloscope	634	Video CRT Monitor	1978
650	Tektronix	Audio/Video	650HR	NTSC color video monitor	1971
651	Tektronix	Display	651	PAL color video monitor	1972
652	Tektronix	Display	652	PAL-M color video monitor	1973
655	Tektronix	Display	655	NTSC/PAL color video monitor	1972
656	Tektronix	Display	656	SECAM color video monitor	(?)
7A12	Tektronix	Plug-in	7A12	120 MHz dual-channel amplifier	1969
FG504	Tektronix	Plug-in	FG504	40 MHz function generator	1976

Datasheet

• Tektronix 155-0032-00 Datasheet (PDF)

Diagrams

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  155-0032-01

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  155-0032-01

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  155-0032-01

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  Block diagram

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  155-0032-00 schematic shown in the 7A12 schematic

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  Comparison of 155-0032-00, 155-0216-00, and 155-0217-00 diagrams