M377
The Tektronix M377 (P/N 165-2129-03,165-2089-06,155-2089-05) is an amplifier monolithic integrated circuit designed by John Addis.
Its initial use was in the 11A16, 11A32, 11A33, 11A34 and 11A52 plug-ins.
About the M377, John Addis says:
The M377 is a single-channel "plugin on a chip" with 0 V common mode input and output voltages, excellent variable gain control, two four-pole bandwidth limits, and three outputs which could be separately inverted and turned on or off.
It was the first wideband analog IC with level shift on chip (allowing 0 V common mode input and output and without PNP transistors), first wideband amplifier with any on-chip bandwidth limit selection (it has two), first to have more than three fixed gain settings (it has six), first to require only one transient response adjustment (it has no thermals), and the first to have a highly linear relationship between a control voltage and gain. It also has excellent overdrive recovery with virtually no thermal tails. The M377 uses feedback to eliminate thermal "tails" for exceptionally clean transient response and excellent gain stability with temperature.
(See also John's comments on the M777 successor.)
Later, the M377 and M777 were also used in several other Tek instruments.
If the instrument has more than 300 MHz bandwidth at 1 mV/div sensitivity,
it can be assumed to be using the M777 which makes use of Tek's later IC fabrication process
that provides transistors with higher FT.
The M377 and M777 are in the following instruments based on the specified bandwidth at 1 mV/div:
| 2245 | 2245A | 2247 | 2247A | 2252 |
| AM503A | AM503B | |||
| TDS410 | TDS420 | TDS460 | ||
| TDS520 | TDS520A | TDS524A | ||
| TDS540 | TDS540A | TDS544A | ||
| TDS620B | TDS644B | |||
| TDS654C |
| TDS520B | TDS520C | TDS520D | TDS540B | TDS540C | TDS540D | TDS580D |
| TDS680B | TDS680C | TDS684A | TDS684B | TDS684C | ||
| TDS714L | TDS724A | TDS724C | TDS724D | TDS744A | TDS754C | TDS754D |
| TDS784A | TDS784C | TDS784D |
Links
- John Addis, Versatile Analogue Chip for Oscilloscope Plug-ins. Electronic Engineering, London, August/September 1988.
- M377 Component Specification
Packaging of the M377
11000 series instruments and the AM503A and AM503B use a 1.22 cm square, flat ceramic package compatible with the Hypcon connector. The ceramic rests on a heat sink supplied by the instrument’s chassis. The ceramic has only thin film conductors. There are no resistors or capacitors on the ceramic except for a 50 ohm input termination resistor, three other resistors, and diode bridge in the 11A52.
TDS series oscilloscopes use a J lead package with a tall heat sink (155-0378-00/01). The package is soldered to the circuit board.
All three outputs have three sets of laser trimmable resistors. The output impedance can be trimmed to 50 ohms, 100 ohms, or 200 ohms per side of the differential output. The laser trimming takes place when the M377 is still in the wafer stage.
To my knowledge, the outputs were never trimmed to 50 ohms. Had this been done, it could have resulted in a fast single-channel amplifier.
When trimmed to 100 ohms, two separate M377s can be connected together (the outputs in parallel) to make a two channel amplifier with a 50 ohm per side output impedance, as in the 11A32. The two M377s are in separate ceramic packages.
Rather than create a new part number for a 50 ohm per side version in the 11A33 (single-channel, 150 MHz differential comparator plugin), the designer chose to use the 100 ohm version and add 100 ohm resistors (in parallel with each output) on the 11A33 circuit board.
The 200 Ω output impedance version is used in the the four-channel 11A34 (50 Ω resulting in four paralleled outputs). The four M377s are in separate ceramic packages.
The nearly complete M377 schematic (with SPICE node numbers) is available on this page. A SPICE file is available.
Tek part numbers:
| Instrument | Instrument SN range | Part Number | Output R/side | Components on ceramic hybrid |
|---|---|---|---|---|
| 11A32 | B010100 - B031028 | 165-2089-03 | 100 Ω | M377 chip only |
| 11A32 | B031029 - up | 165-2089-05 | 100 Ω | M377 chip only |
| 11A33 | B010101 - up | 165-2089-05 | 100 Ω | M377 chip only |
| 11A34 | B010100 - B031044 | 165-2089-04 | 200 Ω | M377 chip only |
| 11A34 | B031045 - up | 165-2089-06 | 200 Ω | M377 chip only |
| 11A52 | B010100 - B010179 | 165-2129-02 | 100 Ω | Diode bridge + 50 Ω input R + M377 chip |
| 11A52 | B010180 - up | 165-2129-03 | 100 Ω | Diode bridge + 50 Ω input R + M377 chip |
| AM503A | B010101 - up | 165-2456-00 | 100 Ω | M377 chip only aka M694 (relaxed DC bal spec) |
| AM503B | B010101 - up | 165-2456-00 | 100 Ω | M377 chip only aka M694 (relaxed DC bal spec) |
Output Control Signals
The M377 has one input (differential) and three identical differential (but separately controllable) outputs. Each output has a its own control pins for:
- Output invert
- Output enable. When an output is disabled, it has no offset and maintains the specified termination impedance. That is, the internal parallel output termination remains connected, but the signal current is shut off. The self-calibration of 11k systems makes use of this property to calculate the main frame's input offset.
- High-frequency adjustment. The HF ADJ pins have 2 kΩ input resistance to ground. The nominally acceptable inputs are ±1 V to ground. Because the input resistance tracks the nichrome standard resistors inside the chip, the input is actually current sensitive, and does not depend on the M377's nichrome sheet resistance. This current affects the standing current in a feedback amplifier and hence its open loop gain. At low frequencies, the gain of the M377 is determined entirely by resistor ratios. At high frequencies, there is phase shift and changing the open loop gain will also change the closed loop gain at high frequencies and hence the transient response at the highest frequencies.
Var Gain Control Signal
The M377 has a single VAR GAIN control input, which affects all three outputs. This control signal has a range of −1 V to +1 V. −1 V results in 0 gain. +1 V results in full gain.
165-2089-xx Pinout
In the 11A32, 11A34, and 11A52, pairs of 165-2089-xx IC are placed on the board so that their outputs are facing one another, allowing their outputs to be wired in parallel with a minimum of board complexity and asymmetry. The function of the three output channels varies depending on the rotational orientation of the M377 on the board.
- Output 1 (pins 25 and 26) is either AUX SIG (aka AUX TRIGGER) or DISPLAY,
- Output 2 (pins 22 and 23) of all 165-2089-xxs are the TRIGGER signals.
- Output 3 (pins 19 and 20) is either AUX SIG (aka AUX TRIGGER) or DISPLAY.
Two 165-2089-xx M377 ICs facing one another in an 11A52. Output 1 of U310 is in parallel with output 3 of U410. Output 3 of U310 is in parallel with output 1 of U410.
Note that in the 11A32 and 11A34, the HF ADJUST control voltages are not set identically for the three outputs. The reason for this is that the DISPLAY and TRIGGER outputs are in parallel with the corresponding output from another M377, which forms a broadband termination. In contrast, the AUX SIG outputs are not combined, and therefore have ¼ W resistors on the PCB, shunting to ground. The ¼ W resistors become inductive at high frequencies, so the optimal HF adjustment for the AUX SIG output is different than for the DISPLAY and TRIGGER outputs.
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Pin function legend
Power pins Ground pins HF signals TTL digital control signals analog control signals
Pictures
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M377 in an 11A52, as U310 and U410. Each M377 chip has a differential output impedance of 200 Ω. The two chips' outputs are in parallel, driving the output pins of the plug-in with a differential impedance of 100 Ω, or 50 Ω per side.
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Two M377 chips (packaged as part number 165-2129-03) in an 11A52
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M377 die
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M377 Die pad names and numbers
