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 was 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, first to have more than two fixed gain settings (it has six), 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.

(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 f_t.

The M377 and M777 are in the following instruments based on the specified bandwidth at 1 mV/div:

M377

2245	2245A	2247	2247A	2252
AM503A	AM503B
TDS410	TDS420	TDS460
TDS520	TDS520A	TDS524A
TDS540	TDS540A	TDS544A
TDS620B	TDS644B
TDS654C

M777

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.

TDS series oscilloscopes use a J lead package with a tall heat sink. The package is soldered to the circuit board.

The 200 Ω output impedance of the version for the four-channel 11A34 (50 Ω resulting with four paralleled outputs) is achieved in the laser trimming stage of wafer production.

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 differential outputs which are identical circuits. 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.
• 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, not that it makes much difference. 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 values. At high frequencies, there is phase shift and changing the open loop gain will also change the closed loop gain, hence the transient response.

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 purpose of the three output channels varies depending on the rotational orientation of the IC 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-xx ICs are the TRIGGER signal.
• 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.

Pin Function Notes 1 GP0 gain select bit 0 2 STB data strobe for gain and bandwidth limit 3 +15 V 4 +Vin 5 Analog ground 6 −Vin</in> 7 Analog ground 8 Var Gain 9 −5 V 10 −5 V 11 Output 1 Invert 12 Output 1 Enable

Pin Function Notes 13 Analog Ground 14 +5 V 15 Output 2 Invert 16 Output 2 Enable 17 Output 3 Invert 18 Output 3 Enable 19 −Output 3 20 +Output 3 21 Output 3 HF Adjust See "High-frequency adjustment" above 22 −Output 2 23 +Output 2 24 Output 2 HF Adjust See "High-frequency adjustment" above

Pin Function Notes 25 −Output 1 26 +Output 1 27 Output 1 HF Adjust See "High-frequency adjustment" above 28 Ground 29 Ground 30 Ground 31 +5 V 32 −5 V 33 BP1 bandpass select bit 1 34 BP0 bandpass select bit 0 35 GP2 gain select bit 2 36 GP1 gain select bit 1

Pin function legend

Power pins

Ground pins

HF signals

TTL digital control signals

analog control signals

Pictures

• 

  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.

• 

  Two M377 chips (packaged as part number 165-2129-03) in an 11A52

• 

  M377 die

• 
• 

  M377 Die pad names and numbers

Schematics

• Tektronix M377 Stage 1 Schematic (PDF)
• Tektronix M377 Stage 1 Control Schematic (PDF)
• Tektronix M377 Stage 2 Schematic (PDF)
• Tektronix M377 Stage 2 Control Schematic (PDF)
• Tektronix M377 Stage 3 Schematic (PDF, rough)