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11A52: Difference between revisions
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Each input channel has a separate 50 ohm attenuator containing, two X10 attenuators, a skin effect correction network, an AC coupling capacitor, a signal pickoff for the input protection network and a switch selecting the calibrator or signal input. In normal operation the calibrator signal to the attenuator is instead connected to ground. | Each input channel has a separate 50 ohm attenuator containing, two X10 attenuators, a skin effect correction network, an AC coupling capacitor, a signal pickoff for the input protection network and a switch selecting the calibrator or signal input. In normal operation the calibrator signal to the attenuator is instead connected to ground. | ||
The 11A52 uses custom Tektronix-made chips including the [[155-0076-00]] (M94 overload detector) and [[M377]] amplifier | The 11A52 uses custom Tektronix-made chips including the [[155-0076-00]] (M94 overload detector) and [[M377]] amplifier integrated circuit. | ||
The signal output of the attenuator feeds | The signal output of the attenuator each feeds a hybrid through a (blue) 50 ohm transmission line, one per input channel. The hybrid looks like packaged M377s found in other instruments. It contains a 50 ohm termination resistor, a diode bridge that protects the M377 from transients too fast for the input relay, and an [[M377]] amplifier C. The input signal is connected to the + input of the [[M377]] amplifier. The cable lengths set a standard delay per plugin. | ||
The M377's − input is connected to the ACVS (Analog Control Voltage System) output. | The M377's − input is connected to the ACVS (Analog Control Voltage System) output. | ||
The (differential) display outputs of the two amplifiers are hard-wired in parallel and drive the mainframe’s 50 Ω per side input impedance. The same is true of the trigger outputs of the two amplifiers. | The (differential) display outputs of the two M377 amplifiers are hard-wired in parallel and drive the mainframe’s 50 Ω per side input impedance. The same is true of the trigger outputs of the two amplifiers. | ||
The version of the M377 used in the 11A52 has a 100 Ω output impedance per side so that two of them in parallel create a source impedance of 50 Ω per side. | The version of the M377 used in the 11A52 has a 100 Ω output impedance per side so that two of them in parallel create a source impedance of 50 Ω per side. | ||
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See also the block diagram below. | See also the block diagram below. | ||
The 11A52 is very similar to the 11A32. There are a few differences. The difference in bandwidth (600 MHz vs 400 MHz) is due almost entirely to the difference in input attenuators. The 11A52 50 Ω is attenuator is passive and contains no amplifier. Additionally the 11A52's M377 sees a 25 ohm source impedance (a terminated 50 ohm transmission line). The 11A32's M377 is driven by the 50 ohm output impedance of the [[M473]]. | |||
The [[11A32]] and [[11A34]] have only one transient response adjustment. This adjustment affects the high frequency response of all six of the M377's fixed gain settings. The 11A52 has the added luxury of a high frequency adjustment for each of the M377's six gain settings to optimize the response at each setting. These settings are manually set under computer control and stored in NVRAM. They need to be reset when the 11A52's NVRAM is replaced. The NVRAM's internal battery typically lasts 20 to 30 years. | |||
If you care to write down the twelve calibration constants while the NVRAM is still alive, you may simply enter them into the new NVRAM. If you do not write them down, you may observe the transient response and set the calibration constants via a personal computer. Instructions for this are found at [[11A-series plug-in NVRAM replacement]] | |||
===Digital=== | ===Digital=== | ||
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In the 11A52, the digital output of the M94 overload detectors (one per channel) are received by the microprocessor. | In the 11A52, the digital output of the M94 overload detectors (one per channel) are received by the microprocessor. | ||
If overload is detected, software running in the microprocessor switches the input relay | If overload is detected, software running in the microprocessor switches the input relay to remove the signal from the 50 Ω attenuator. | ||
This is in contrast to the [[485]], where the M94 directly controls the input relay. | This is in contrast to the [[485]], where the M94 directly controls the input relay. | ||
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The outputs are checked by the self-check software routine. | The outputs are checked by the self-check software routine. | ||
The | The 11A52 also contains a Dallas Semiconductor DS1220Y NVRAM storing last settings, calibration constants, and instrument serial number. | ||
The DS1220Y contains a battery with a typical life time of 20-30 years. | The DS1220Y contains a battery with a typical life time of 20-30 years. | ||