pll report
TRANSCRIPT
Report on Voltage Control
Oscillator and Phase Lock Loop
Nguyen Quang Hai
June 10, 2015
Contents
1 Introduction 1
2 Voltage Control Oscillator (VCO) 2
2.1 Colpitts oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.2 Control the frequency by diode capacitor . . . . . . . . . . . . . . . . . . . . 3
3 Comparision between the new and the old circuit 7
3.1 Phase Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Low pass filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3 Voltage control oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.4 Phase lock loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4 Result of the new circuit only 13
4.1 Phase Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2 Low pass filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3 Voltage control oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.4 Phase lock loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5 Circuit schematic 19
5.1 Phase detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.2 Low pass filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.3 VCO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
i
5.4 Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.5 BNC connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.6 Additional components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
ii
Chapter 1
Introduction
This report discusses the making of the voltage control oscillator (vco) and the comparision
between the new and the old circuit.
1
Chapter 2
Voltage Control Oscillator (VCO)
2.1 Colpitts oscillator
The main part of the VCO is the oscillator, and in this circuit, Colpitts oscillator is used.
Figure 2.1: Colpitts Oscillator
Figure 2.1 shows the basic configuration of the Colpitts oscillator. Resistors RB, RC are used
to bias the transistor. The resonance frequency of this oscillator can be found by:
2
f0 =1
2π√L1C
(2.1)
And the capicitance C can be calculated by the following formula:
C =C2C4
C2 + C4
=1nF · 10nF
1nF + 10nF= 0.91nF (2.2)
Then the resonance frequency can be found as follow:
f0 =1
2π√L1C
=1
2π√
12.6uH · 0.91nF= 1.486MHz (2.3)
To control the frequency of this circuit, diode capacitor is used. The realization of this circuit
is discussed in the next section.
2.2 Control the frequency by diode capacitor
Figure 2.2 shows the schematic of the VCO. From the previous section, the resonance fre-
quency of this circuit can be calculated as following:
f0 =1
2π√L1Ctot
(2.4)
And Ctot can be described as: Ctot = C4 series (C2 // (C1 series n× Cd)) (n is the number
of diode capacitance).
3
Figure 2.2: Circuit schematic of VCO
From the circuit description, Ctot can be obtained as following:
Ctot =20nCdC1 + C2
1
12nCd + 11C1
(2.5)
C1 = C2 = 110C4 is used for simplification and Cd is the capacitance of the diode capacitor.
And the number of used diode capacitors can be derived as following:
n =11C1Ctot − 10C2
1
20Cd − 12CdC1
(2.6)
From formula 2.4, to obtain the frequency of f = 1.37MHz, Ctot must be equal 1.0711 nF.
From Formula 2.6 and from Figure 2.3, the number of diode needed at the reversed voltage
Ust = 6V is n = 7.
4
Figure 2.3: Diode capacitance as the function of reserved voltage
Figure 2.4 and Table 2.1 show the result of measurement of the VCO. It can be seen that f
is equal 1.37 MHz at Ust is approximately at 2.5V not at 6V as the calculation above. This
result will be used to evaluate the behavior of the phase look loop.
5
Table 2.1: Measured resonance frequency
Ust f/MHz0 1.322 1.364 1.406 1.428 1.4410 1.4512 1.4614 1.4716 1.47
Figure 2.4: Static modulation characteristic of the VCO
6
Chapter 3
Comparision between the new and the
old circuit
3.1 Phase Detector
Table 3.1 and Figure 3.1 show the comparision between the old and the new circuit. There is
little difference between two curves, eventhough the old circuit works at the input frenquency
of 1.38 MHz meanwhile the new one operates at 1.37 Mhz. The important point is that, at
90 degree, the output voltage of the new circuit is 0V, which satifies the requirement.
7
Table 3.1: Transfer function of phase detector
Phase/degree Uout/V original Uout/V new0 0.57 0.5710 0.56 0.5620 0.54 0.5330 0.50 0.4940 0.44 0.4450 0.37 0.3860 0.30 0.2970 0.20 0.2080 0.11 0.1090 0.01 0.00100 -0.08 -0.10110 -0.18 -0.18120 -0.27 -0.27130 -0.35 -0.35140 -0.42 -0.42150 -0.47 -0.46160 -0.52 -0.52170 -0.54 -0.54180 -0.55 -0.55
Figure 3.1: Transfer function of phase detector
8
3.2 Low pass filter
In this part, the transfer function of the new and the old low pass filter are compared. From
Figure 3.2, the cut off frequency of the old circuit fc equals 260kHz and the new one’s is 300
kHz.
Table 3.2: Transfer function of low pass filter
f/Hz Uout,rms/mV original Damping/dB original Uout,rms/mV new Damping/dB new10 1000 20 1000 2020 1000 20 1000 2050 1000 20 1000 20100 1000 20 1000 20200 1000 20 1000 20500 1000 20 1000 201k 1000 20 1000 202k 1000 20 1000 205k 1000 20 1000 2010k 1000 20 990 19.920k 1000 20 980 19.850k 960 19.7 960 19.6100k 920 19.3 920 19.3200k 810 18.2 820 18.3500k 490 13.8 580 15.3800k 290 9.3 280 8.9
1,000k 200 6.0 160 4.0
9
Figure 3.2: Transfer function of low pass filter
3.3 Voltage control oscillator
From the old circuit, the modulation characteristic is linearised at operation point Ust = 6V
and the constant k0 has the result:
k0 =∆ω
∆Ust
=2π∆f
∆Ust
=2π × 0.04Mhz
4V= 2π × 104rad/V s (3.1)
For the new circuit, the modulation characteristic is linearised at operation point Ust = 2V
and the constant k0 has the result:
k0 =∆ω
∆Ust
=2π∆f
∆Ust
=2π × 0.08Mhz
4V= 4π × 104rad/V s (3.2)
10
Table 3.3: Static modulation characteristic of the VCO
Ust f/MHz original f/MHz new0 1.30 1.322 1.33 1.364 1.36 1.406 1.38 1.428 1.40 1.4410 1.41 1.4512 1.42 1.4614 1.42 1.4716 1.43 1.47
Figure 3.3: Static modualation characteristic of the VCO
11
3.4 Phase lock loop
This section shows the result of the closed control loop. The center frequency of the new
circuit is fc = 1.37MHz and it has a better Lock range and Capture range than the old one.
Table 3.4: Result of the closed control loop
Original circuit New circuitfOH/MHz 1.408 1.427fUH/MHz 1.388 1.378fUL/MHz 1.371 1.358fOL/MHz 1.334 1.311
Lock range/KHz 74 116Capture range/KHz 17 20
12
Chapter 4
Result of the new circuit only
4.1 Phase Detector
• Set amplitude of 2 generators to Uss1 = 4V, Uss2 = 8V .
• Frequency of both signal is set to 1.37MHz.
The constant kD of the phase detector:
kD =∆Uout
∆Φ=
0.37V − (−0.35V )130−50180
× πrad= 0.516V/rad (4.1)
13
Table 4.1: Transfer function of phase detector
Phase/degree Uout/V0 0.5710 0.5620 0.5330 0.4940 0.4450 0.3860 0.2970 0.2080 0.1090 0.00100 -0.10110 -0.18120 -0.27130 -0.35140 -0.42150 -0.46160 -0.52170 -0.54180 -0.55
Figure 4.1: Transfer function of phase detectorr
14
4.2 Low pass filter
• Changing the input frequency from 10Hz to 1MHz while keeping the amplitude con-
stant at Urms = 100mV .
• The cut off frequency of the low pass filter is fg = 300kHz.
Table 4.2: Transfer function of low pass filter
f/Hz Uout,rms/mV Damping/dB10 1000 2020 1000 2050 1000 20100 1000 20200 1000 20500 1000 201k 1000 202k 1000 205k 1000 2010k 990 19.920k 980 19.850k 960 19.6100k 920 19.3200k 820 18.3500k 580 15.3800k 280 8.9
1,000k 160 4.0
15
Figure 4.2: Transfer function of low pass filte
4.3 Voltage control oscillator
• Adjust Ust from 0V to 16V, draw the transfer function.
• Linearise at operation point Ust = 2V and determine constant k0.
The result of k0:
k0 =∆ω
∆Ust
=2π∆f
∆Ust
=2π × 0.08Mhz
4V= 4π × 104rad/V s (4.2)
16
Table 4.3: Static modulation characteristic of the VCO
Ust f/MHz0 1.322 1.364 1.406 1.428 1.4410 1.4512 1.4614 1.4716 1.47
Figure 4.3: Static modualation characteristic of the VCO
4.4 Phase lock loop
Adjust the input signal to f = 1.37MHz and U = 4V. Table 4.4 shows the result of the
measusement.
17
Table 4.4: Result of the closed control loop
New circuitfOH/MHz 1.427fUH/MHz 1.378fUL/MHz 1.358fOL/MHz 1.311
Lock range/KHz 116Capture range/KHz 20
18
Chapter 5
Circuit schematic
5.1 Phase detector
Figure 5.1: Schematic of phase detector
19
Figure 5.2: Layout of phase detector
20
5.2 Low pass filter
Figure 5.3: Schematic of low pass filter
Figure 5.4: Layout of low pass filter
21
5.3 VCO
Figure 5.5: Schematic of VCO
Figure 5.6: Layout of the board
22
5.4 Board
Figure 5.7: Layout of the board
Figure 5.8: Picture of the board
23
5.5 BNC connector
MUILTICOMP 13-22 Buchse Flansch BNC 50 OHM
Bestellnummer: 1169700 from de.farnell.com
Figure 5.9: BNC connector
24
5.6 Additional components
Figure 5.10: Additional components
• 1: C = 1µF
• 2: C = 22pF,R = 10MΩ
• 3: C = 100nF,R = 5.1kΩ
25