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155-0032-00: Difference between revisions
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The Tektronix '''155-0032-00''' is a differential amplifier chip made by Tektronix. | The Tektronix '''155-0032-00''' is a differential amplifier chip made by Tektronix. | ||
It is packaged in a 16-pin DIP. | It is packaged in a 16-pin DIP. | ||
Regarding the 155-0032-xx, John Addis said, | |||
<blockquote> | |||
The 155-0032-00’s IC process had an FT of 1.0 or 1.2GHz (don’t remember), rather inadequate for the job. | |||
The on-chip resistors were diffused and thus had | |||
too poor a TC and tolerance for use as gain-setting resistors. | |||
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As you can see, | |||
there are two separate gain selections 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 5mV/div to match that at all other sensitivities, controlled elsewhere. | |||
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<br> | |||
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 of the output signal. | |||
This same pair of transistors also enables variable gain by allowing | |||
a controlled amount of cross-coupling of the signal. | |||
<br> | |||
<br> | |||
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. | |||
<br> | |||
<br> | |||
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.) | |||
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<br> | |||
The M377 was a single channel plugin on a chip with 0V common mode input and output voltages, | |||
excellent variable gain control, two four pole bandwidth limits, | |||
three outputs which could be separately inverted and turned on or off. | |||
<br> | |||
<br> | |||
It was the first wideband analog IC with level shift on chip (allowing 0V common mode input and output and without PNP transistors), | |||
first wideband amplifier with any on-chip bandwidth limit selection, first to have more than two fixed gain settings (it has six), | |||
and 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. | |||
</blockquote> | |||
The input differential amplifier's emitters are brought out to pins 1 and 16. | The input differential amplifier's emitters are brought out to pins 1 and 16. | ||