Source Block Section - Agilent Technologies 4284A Service Manual

3-9-3. SOURCE BLOCK SECTION

The source block section is composed of the A4 high power amplifier/de bias and the AS
sig nal source boards. The A4 board is only installed for the Option 001 .
The AS signal source board generates the AC voltage (S mVrms to 1 Vrms), and also gener­
ates 1 .SV/2 .0V DC voltages. The AS signal source consists of three crystal oscillators , the
programmed N divider, the quasi-sine wave generator, the attenuator, the D-A Converter, the
dc bias voltages (1 .S V /2.0 V) , the output amplifier, and the source resistor. (Refer to Figure
3-S.)
TP2
+ M
Quasi-Sine Wave
Generator
FCLK
Figu re 3-S. Sig nal Source (AS) Simplified Block Diagram
The crystal oscillators are 1 9 .2 MHz, 1 6 .0 M H z , and 1 S .36 M H z. One of three crystal oscilla­
tors (FCLK) is selected and the output signal is divided by N using the programmed N di­
vider. The d ivided signal is applied to the quasi-sine wave generator which generates a
digital sinewave (staircase waveform). The digital sinewave' s frequency is the same as the
output test freq uency. So the avai lable test frequencies (F) are calucu lated using the follow­
ing fomula.
The digital sinewave is filtered by the LPF, and the filtered sine wave is input to the D-A
converter (DAC) as a voltage reference. So the 4284A covers various test signals with a high
resolution by using both the DAC and the attenuator.
TP3 TP6
(
F FCLK / N x M )
=
Where,
FCLK: 1 9 .2 M Hz, 1 6 .0 M H z, 1 S.36 M H z
N : 2 t o 409S (integer)
M :
8, 1 6 , 32, 64, 1 28 , 2S6
3-25
100
OUTPUT
2 V
1.5 V
OFF
(DC BIAS)