信号发生器的基本知识概述

fL = 2f1 - f2
Source Basics
fU = 2f2 - f1
frequency
Copyright 2000
Applications & Critical Specifications
Receiver Testing
Receiver Selectivity
in-channel signal (modulated signal) IF signal
Output Attenuator
by X Ref Osc
Sampler
YIG Oscillator Phase Detector
Frac-N
Tuning Coils
ALC Driver
Phase Detector VCO
Synthesizer Section
ALC Detector
Output Section
...Frequency

Range: Range of frequencies covered by the source Resolution: Smallest frequency increment. Accuracy: How accurately can the source frequency be set.
Source Basics
Copyright 2000
Applications & Critical Specifications
Amplifier Testing
f1
Intermodulation Distortion f2
isolator
DUT
output RF
f1
f2
test system third order products will also fall here spurious signals from source can corrupt measurement
RF CW Block Diagram
Synthesizer Section
Frac-N
Output Section
ALC Modulator
Phase Detector Output Attenuator
wk.baidu.com
VCO
divide by X Reference Oscillator
ALC Driver
ALC Detector

from synthesizer section
ALC Modulator
Output Attenuator source output
Output Attenuator
–mechanical
or
electronic –provides attentuation to achieve wide output range (e.g. -136dBm to +13dBm)
Voltage
t aging = t cal =
f CW =
Frequency
Hz
Source Basics
Copyright 2000
CW Source Specifications
...Amplitude

Range (-136dBm to +13dBm) Accuracy (+/- 0.5dB) Resolution (0.02dB) Switching Speed (25ms) Reverse Power Protection
Frequency
Source Basics
Copyright 2000
Agilent Families of CW Generators
RF
Agilent 8662/63 family
100 KHz - 2.5 GHz Low in channel noise AM/FM/Phase/Pulse
How accurate is this number?
Source protected from accidental transmission from DUT What ismax P DUT out?
Voltage
min
What is P Frequency
out?
Source Basics

Types of sources CW Swept Signal Generator Block Diagrams Applications Specifications
Source Basics
Copyright 2000
CW Source Specifications
PLL / Fractional - N ...suppresses phase noise phase noise of source
phase-locked-loop (PLL) bandwidth selected for optimum noise performance
reference oscillator

(for system)
Receiver Testing
– Spurious
spurious level accuracy

Source Basics
Copyright 2000
Applications & Critical Specifications
As a Local Oscillator
over a range of frequencies – may be phase continuous

Signal Generator
– adds
modulation – produces “real world” signal
Source Basics
Copyright 2000
Agenda
5MHz
to output section Phase Detector VCO
X
2
931 MHz
multiplier
5MHz
from reference section
465.5 MHz
Source Basics
Copyright 2000
RF CW Block Diagram
Synthesizer Section
CW output measured as dBc/Hz
frequency
TRACE A: Ch1 PM PSD A Marker 10 000 Hz
75 dBc/Hz
LogMag 5 dBc/div
-105 dBc/Hz
-125 dBc/Hz
1k
10k
Copyright 2000
100k
Source Basics
+/- 0.5ppm
+/- 0.001 ppm
Source Basics
Copyright 2000
RF CW Block Diagram
Synthesizer Section
...produces accurate, clean signals
N = 93.1
Frac-N Front panel control
EXAMPLE
Accuracy =
+ _ f CW * t aging * t cal CW frequency = 1 GHz aging rate = 0.152 ppm/year time since last calibrated = 1 year _ = Accuracy + 152
Uncertainty
Optional External Reference Input
Reference Oscillator (TCXO or OCXO)
Aging Rate Temp.
TCXO +/- 2ppm/year +/- 1ppm
OCXO +/- 0.1 ppm /year +/- 0.01 ppm
Line Voltage
Copyright 2000
CW Source Specifications
...Spectral Purity

Phase Noise Residual FM Spurious
CW output
Residual FM is the integrated phase noise over 300 Hz - 3 kHz BW sub-harmonics
phase noise
non-harmonic spur ~65dBc
harmonic spur ~30dBc
0.5 f0 2 f0 Source Basics
f0
Copyright 2000
CW Source Specifications
... Spectral Purity: Phase Noise
RF 3-6 GHz Microwave 20-50 GHz Millimeter 300 GHz
Source Basics
Copyright 2000
Types of Sources

CW
– generates
a single frequency, fixed sine wave

Swept
– sweeps
ALC Driver
ALC Detector
ALC = automatic level control
Copyright 2000
Source Basics
mWave CW Block Diagram
Reference Section
Frac N
Phase Det VCO
ALC Modulator
Copyright 2000
Agenda

Agilent 8664/65 family
100 MHz - 6 GHz Low out channel noise AM/FM/Pulse.

Microwave
Agilent 83711/12B family
10 MHz - 20 GHz CW only

Source Basics
Voltage
Time
Voltage
Frequency
Oscilloscope
Spectrum Analyzer
This is the ideal output: most specs deal with deviations from the ideal and adding modulation to a sine wave
DUT
IF signal transmitter output
poor frequency accuracy will cause transmitter to be at the wrong frequency
poor phase noise spreads energy into adjacent channels
Source Basics
Copyright 2000
Applications & Critical Specifications

Local Oscillator
– phase
noise – frequency accuracy

Amplifier Distortion
– spurious
– TOI
out-of-channel signal (CW or modulated signal)
DUT
source output IF Rejection Curve
Level (dBm)
spur from source and/or high levels of phase noise can cause a good receiver to fail
Agenda
Types of sources CW Swept Signal Generator Block Diagrams Applications Specifications

Source Basics
Copyright 2000
Sources Generate Sine Waves
20logN
phase detector noise
broadband noise floor
VCO noise
Source Basics
frequency
Copyright 2000
RF CW Block Diagram
Output Section

ALC
–maintains
output
power by adding/subtracting power as needed
Reference Section
ALC = automatic level control
Source Basics
Copyright 2000
RF CW Block Diagram
Reference Section
to synthesizer section Phase Detector divide by X