Agilent Technologies 35670-90066 manual A5 Analog

Channel 1 Track & Hold

Channel 2 Track & Hold

Channel 3 Track & Hold

Channel 4 Track & Hold

Channel Switch

1st Pass Circuit

ADC Controller

Circuit Descriptions	Agilent 35670A
A5 Analog

A5 Analog

The A5 Analog assembly converts the analog input from the A1 Input assembly or A2 Input assemblies to 16-bit serial, digital data. The Analog assembly also converts digital data from the A6 Digital assembly to the analog source output.

The input conversion process passes the analog inputs from all active channels through an 8-bit ADC (analog-to-digital converter) twice adding dither (noise) to improve linearity and the accuracy of low-level signals. All active inputs are sampled simultaneously and held until all have been converted. For the first-pass conversion, the input is scaled then converted to 8-bit serial, digital data. Dither is added to the first-pass data and the sum is converted to an analog voltage. The analog voltage is subtracted from the input and the difference is scaled then converted to 8-bit, serial data in the second pass. The first-pass and second-pass values are added to get the final 16-bit data word. A third conversion clears the 8-bit ADC.

Holds a voltage sample of the channel 1 input signal for the period of time required by the ADC circuits to digitize the voltage.

Holds a voltage sample of the channel 2 input signal for the period of time required by the ADC circuits to digitize the voltage.

Holds a voltage sample of the channel 3 input signal for the period of time required by the ADC circuits to digitize the voltage.

Holds a voltage sample of the channel 4 input signal for the period of time required by the ADC circuits to digitize the voltage.

For the two channel analyzer, the Channel Switch multiplexes the channel 1 and channel 2 input signals during two channel measurements . During single channel measurements, the channel 1 and channel 2 signals are not multiplexed. Instead, the Channel Switch is fixed to the output of the Channel 1 Track & Hold. For the four channel analyzer, the Channel Switch multiplexes the channel 1 and channel 2 input signals during two channel measurements. During four channel measurements, the Channel Switch multiplexes the channel 1, 2, 3, and 4 input signals. The output of the Channel Switch is converted to a 16-bit digital word by passing the signal through an 8-bit ADC twice.

Divides the Channel Switch output by four and level shifts it to the 8-bit ADC input range of 0 to −0.5 V.

Adds dither (noise) to the first pass signal to increase the accuracy and reduce the non-linearity of the Analog-to-Digital conversion. After the first pass signal is filtered and converted to an

8-bit word, the ADC Controller adds the dither and outputs a 16-bit word to the 2nd Pass DAC. After the second pass signal is filtered and converted to an 8-bit word, the ADC Controller adds the second pass word to the first pass word to obtain a 16-bit data word. The ADC Controller then sends the converted data as ADDATA to the A6 Digital assembly. The ADC Controller also detects an ADC overload when the signal to the analog-to-digital converter is too high. The overload information is sent as ADCOL and ADCUL to the A6 Digital assembly.

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