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/dc bias and the A5
signal source boards. The A4 board is only installed for the Option 001.
The A5 signal source board generates the AC voltage (5 mVrms to 1 Vrms), and also gener-
ates 1.5V/2.0V DC voltages. T h e A5 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 (1.5 V/2.0 V), the output amplifier, and the source resistor. (Refer to Figure
3-5.)
TP2
0
÷M
X'tal OSC
Quasi-Sine Wave
Generator
FOLK
Figure 3-5. Signal Source (A5) Simplified Block Diagram
The crystal oscillators are 19.2 MHz, 16.0 MHz, and 15.36 MHz. One of three crystal oscilla-
tors (FCLK) is selected and the output signal is divided by N using the programmed N di-
vider. T h e divided signal is applied t o the quasi-sine wave generator which generates a
digital sinewave (staircase waveform). T h e digital sinewave's frequency is the same as the
output test frequency. S o the available test frequencies (F) are caluculated 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. S o the 4284A covers various test signals with a high
resolution by using both the DAC and the attenuator.
7 \ J
TP3 T P 6
0 0
LPF - 4 " . DAC ATT
F = FCLK / ( N x M )
Where,
FCLK: 19.2 MHz, 16.0 MHz, 15.36 MHz
N: 2 to 4095 (integer)
M: 8 , 16, 32, 64, 128, 256
3-25
X 2
100
2 V
1.5 V
OFF
(DC BIAS)
OUTPUT
(_.4)
- 2 -
=3 CA
o ( D
-7 =
CI)
0 U )
= CD
C-)
CD