HP 1GSa/s Digitizing Oscilloscope 16532A manual Introduction Safety Requirements, Acquisition

HP 16532A - Service

6-1. Introduction

The service policy for this instrument is replace- ment of defective assemblies. This service manual contains information for finding a defective assembly. This section contains information for servicing the HP 16532A Oscilloscope Module. Included are a block level theory and procedures for self diagnostics and troubleshooting. If the module or a cable is determined faulty, procedures are provided for module and cable replacement.

6-2. Safety Requirements

Specific warnings, cautions, and instructions are placed wherever applicable throughout the manual. These must be observed during all phases of operation, service, and repair of the module. Failure to comply with them violates safety standards of design, manufacture, and intended use of this module. Hewlett-Packard assumes no liability for the failure of the customer to comply with these safety requirements.

6-3. Recommended Test Equipment

Table 1-3 lists recommended test equipment. Any equipment that satisfies the critical specification given in the table may be substituted for the recommended models.

SECTION VI

Service

6-5. Attenuator Theory of Operation

The channel signals are conditioned by the attenuator/preamps, thick film hybrids containing passive attenuators, impedance converters, and a programmable amplifier. The channel sensitivity defaults to the standard 1-2-4 sequence (other sensitivities can be set also). However, the firmware uses passive attenuation of 1, 5, 25, and 125, with the programmable preamp, to cover the entire sensitivity range.

The input has a selectable 1 MΩ input impedance with ac or dc coupling or a 50Ω input impedance with dc coupling. Compensation for the passive attenuators is laser trimmed and is not adjustable. After the passive attenuators, the signal is split into high-frequency and low-frequency components. Low frequency components are amplified on the main assembly, where they are combined with the offset voltage. The ac coupling is implemented in the low frequency amplifier.

The high- and low-frequency components of the signal are recombined and applied to the input FET of the preamp. The FET provides a high input impedance for the preamp. The programmable preamp adjusts the gain to suit the required sensitivity and provides the output signal to the main assembly. The output signal is then sent to both the trigger circuitry and ADC.

6-4. Module Block Diagram and The- ory of Operation

The following paragraphs contain block level theory of operation. This theory is not intended for component level troubleshooting, rather it is to be used to help isolate a module failure to card level.

The HP 16532A Oscilloscope Module is contained on one board. It runs at a 1 GSa/s digitizing rate, with a 250 MHz single-shot (real-time) bandwidth, 8000 samples per measurement per channel, with 2-channel simultaneous acquisition which is expandable to up to 8 channels. See figure 6-1.

6-6. Main Assembly Theory of Operation

Acquisition

The acquisition circuitry provides the sampling, digitizing, and storing of the signals from the channel attenuators. The channels are identical. The external trigger (ECL) input cannot be displayed. Trigger signals from each channel and the external triggers synchronize acquisition through the time base circuitry. A 100 MHz oscillator and a time base provide system timing and sample clocking. A voltage-controlled oscillator (VCO), frequency divider, and digital

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