Name: Keithley 2015
Brand: Keithley
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Troubleshooting 4-15

Distortion analog circuitry

Refer to Figure 4-5 for the following discussion on distortion analog circuitry.

Figure 4-5

Distortion analog circuitry block diagram

Ampliﬁer ﬁlter

The buffered and scaled AC waveform from the analog circuitry (Figure 4-3) is fed to U309

and U310. U309 and U310 form an ampliﬁer, antialiasing ﬁlter, and DC shifting circuit to con-

dition the AC waveform for the distortion measurement ADC converter.

ADC converter

The distortion measurement circuitry uses a separate ADC converter from the rest of the

DMM measurements (see U165 in Figure 4-3). This ADC is a high-speed, high-resolution, low-

distortion sigma delta type. The ADC digital output is sent to the DSP through opto-isolators

shown in Figure 4-5.

ADC clock

Y301 is a ﬁxed frequency clock that forms the input to U325, an adjustable frequency clock

generator. The output of this generator clocks the ADC, setting the acquisition rate. The clock

generator frequency is set by the microprocessor and is communicated through U314, the

FPGA. The FPGA, U314, is conﬁgured by U315, an EEPROM, upon power-up.

Analog

Circuitry

(See Figure 4-3)

Amplifier Filter

U309, U310

ADC Converter

U311

OSC

Y301

ADC Clock

Generator

U325

FPGA U314

EEPROM

U315

Distortion

Digital

Circuitry

(See Figure 4-4)

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Keithley 2015 Specifications

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