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{{Monolithic IC | |||
|Manufacturer=Tektronix | |||
|Model=M753 | |||
|Part_nos= | |||
|Description=buffer amplifier | |||
|an=an | |||
|Used_in=H2462 | |||
|Designers=John Addis; | |||
}}. A higher-bandwidth (2 GHz) version of the [[M713]] 1 GHz unity-gain buffer amplifier, the M753 is the first amplifier stage in the [[H2462]] input hybrid which is used in several TDS500, TDS600, and TDS700-series scopes. | |||
At the time of the M753's development, [[John Addis]] wrote: | |||
<blockquote> | |||
Long ago, high frequency oscilloscopes had one input attenuator for each calibrated deflection factor. | |||
The [[500-series_plug-ins_(Letter-series_and_1-series)|540 series plugins]], Type [[CA]] and [[L]], are examples from the 1950s. | |||
In order to save money, scope input attenuators have been reduced in number over the years to just three | |||
while amplifiers have added either gain switching or internal attenuation to make up for the required missing deflection factors. | |||
The three attenuators are usually ×1, ×10, and ×100. | |||
The ×1 attenuator is essentially a straight wire or alternatively just a very small attenuation (typically 10%) | |||
to provide protection to the input JFET. It is very difficult to make a single ×100 attenuator, | |||
so the ×100 attenuation is usually a second ×10 attenuator cascaded with the first as needed. | |||
The ×1 attenuator is often in cascade with the other attenuator(s) and may be located at the amplifier’s input. | |||
The high frequency response is strictly a function of the path length from the input BNC connector to the JFET input, | |||
and three inches was considered “short”. | |||
Various damping resistors are placed in the signal path to reduce ringing, | |||
and the attenuator is really a combination quasi-transmission line structure of 75 to 90 ohms impedance | |||
at high frequencies and a high impedance RC divider at low frequencies. | |||
Several years ago, [[Jim Woo]] suggested that it should be possible to improve the performance of our input attenuators | |||
and reduce their cost if the attenuation selection were done in part by selecting separate amplifiers for each attenuator. | |||
Relays select which attenuator is attached to an input line, but only one attenuator at a time is actually connected to the input line. | |||
The amplifier and a relay select which attenuator the output signal comes from. | |||
This was not practical until integrated JFETs became available. See the "New Attenuator Scheme" figure. | |||
There are several advantages inherent in this scheme. | |||
In this configuration, input from the front panel consists of a 50 Ω transmission line | |||
and three different attenuators (×1, ×10, and ×100) are attached to this line. | |||
A single 50 Ω resistor serves to terminate the line in the 50 Ω (input impedance) mode. | |||
This termination is at the end of the input line instead of at the beginning as with previous attenuators. | |||
More commonly now, the 50 Ω termination is at the BNC and all the other attenuators are disconnected in 50 Ω input impedance mode. | |||
</blockquote> | |||
<gallery> | |||
1990-08-23 New Attenuator scheme m753.jpg|New Attenuator Scheme | |||
1990-10-12 M753A Ckt Description for Eng p1.jpg | |||
1990-10-12 M753A Ckt Description for Eng p2.jpg | |||
1990-10-12 M753A Ckt Description for Eng p3.jpg | |||
1990-10-12 M753A Ckt Description for Eng p7.jpg | |||
1990-10-12 M753A Ckt Description for Eng p8.jpg | |||
1990-10-12 M753A Ckt Description for Eng p9.jpg | |||
1990-10-12 M753A Ckt Description for Eng p10.jpg | |||
</gallery> | |||
[[Category:Tektronix-made monolithic integrated circuits]] | [[Category:Tektronix-made monolithic integrated circuits]] |