HP 3562A, Руководство по обслуживанию

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MOD E L 3562A C I RCUIT D E SC R I PT I O N S
6-1 5 A3 2, A34 ANALOG-ta-DIGITAL CONVERTERS
(Refer to ADC Board Block Diagram on figure 6-A32) The ADC board converts analog
data from the in put board i nto 1 3-bit serial data words. The main parts of the ADC are
two variable attenuators and their accompanyi ng am pl ifiers, an anti-al ias filter, a track
and hold circu it, an 8-bit A/D converter (to avoid confusion, the board is referred to as
11
ADC" and the part is cal led
11
A/D converter"), a D/A converter (DAC), and a control ler.
Other c i rcu its on the board incl ude first and second pass circu its and the p rocess switch,
a dc offset D/A converter, an over range/half range c i rcu it, a missed sample c i rcu it, a
diagnostic tester, and sl ave/m aster selection circu its.
The circu its in the d ata path may be divided into analog and digita l . The s ignal is analog
u ntil it passes through the A/D converter. This discussion is divided into analog and digital
sections.
Analog
The signal from the i nput board enters the ADC board th rough )200 and a bal u n and goes
to attenuator #2 (#1 is on the input board). This attenuator is variable in 2 dB steps from
o dB to 1 2 d B. It can also ground the input of the next ampl ifier (for calibration pu rposes).
The configu ration information for th is attenuator and attenuator #3 come from serial-to­
parallel (S/P) shift register U203. This i nformation comes on the board from the input board
and is shifted through U603, U203, and U202. The companion i nput board m ust be installed
for the ADC board to receive configu ration i nformation .
The signal from attenuator #2 goes to amplifier #3. This am pl ifier i s a non-inverting
op amp circuit with a gain of 3. The s ignal from this amp l ifier goes to atte nu ator #3. This
attenuator is identical to attenuator #2 except that instead of selecti ng a grou nded i nput
for the fol lowing ampl ifier it has another step of attenuation, giving it a range of 0 d B
to 1 4 d B i n 2 dB steps.
The purpose of all the ampl ifiers and variab le attenuators up to this po i nt is to assure
that the strength of the signal to the anti-al ias filter does not over d rive it. Refer to table
6-A32a for information conceming attenuator configu ration for a given range seiection.
6-1 1 3