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第 4 章Oscillators

Presenter ：吳壬竹Adviser ： Dr.Chih-Kuo Liang

Date: 96.1.9

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Outline

4.1 Oscillator Fundamentals

4.2 WIEN-BRIDGE Oscillator

4.3 Voltage-Controlled Oscillator

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4.1 Oscillator Fundamentals

Amplification Positive feedback Frequency determining network

AmplifierFrequencySelectivecircuit

OutputInput

Positive feedback

Single frequencyOutput signal

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4.2 WIEN-BRIDGE Oscillator 4.2.1

• OperationRI 510Ω

RF 510Ω

741

R1 6.8kΩ

C1 0.01μF

C2 0.01μF

R2 6.8kΩ

RG 470kΩ

CG 0.1μF

D1

1N914A

MPF102 Q1

Half-waverectifier/filter

Noninverting amplifier

Frequencyselection

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4.2.2• Practical Design Techniques

4.2 WIEN-BRIDGE Oscillator

1. Frequency of oscillation 10.5 kHz

2.Available FET MPF102

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4.2 WIEN-BRIDGE Oscillator

VGS(off)

IDSS(max)＝ RI

(4.2) ＝ 8 V

20 mA

(4.3)

4.2.2• Compute RF and RI.

RF = RI

＝ 400 Ω

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4.2 WIEN-BRIDGE Oscillator

4.2.2• Compute Rectifier and Filter Components.

＝ RGCG

100

fo(4.4)

＝ RGCG

100

10.5 kHz＝ 9.52 ms

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4.2 WIEN-BRIDGE Oscillator

4.2.2• Select the Op Amp.

Slew rate(min) ＝ πfo [ ]VGS(off)2

＋ 0.7 (4.8)

＝ 3.14 x 10.5 kHz [ ]8 V2

＋ 0.7 V

＝ 0.155 V /μs

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4.2 WIEN-BRIDGE Oscillator 4.2.1( 課外補充 )

• Operation RF

R

R

C

C

RA V-

V+

Vo

Z1 Z2

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4.2.2• Numerical Analysis

4.2 WIEN-BRIDGE Oscillator

Z1V+ ＝ Vo Z1 + Z2

＝s2(RC)2 + 3sRC + 1

RCsVo

VoV- ＝ 1 + RF/RA

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4.2.2• Numerical Analysis

4.2 WIEN-BRIDGE Oscillator

˙˙˙

V+ ＝ V- ﹐ s ＝ jω ﹐ RC ＝ τ

11 + RF/RA

＝ -ωτj(1 - ω2τ2)-3ωτ

1 - ω2τ2 ＝ 0

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4.2.2• Numerical Analysis

4.2 WIEN-BRIDGE Oscillator

11 + RF/RA

＝ -3ωτωτ

RF ＝ 2RA

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4.3 Voltage-Controlled Oscillator

741741

741

R1

C1

A1

A2

A3R2

R4 D4

R6

R5

R3D3

D1

D2

D5

D6+Vm

volts

1-520kΩ

2kΩ

10kΩ

5.1kΩ

10kΩ

10kΩ 1N914A

1N914A

1N4735A1N4735A

0.001μF

4.3.1• Operation

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4.3 Voltage-Controlled Oscillator

4.3.2• Numerical Analysis

VUT ＝ VZD2 ＋ VFD1 (4.9)

VLT ＝ － VZD1 － VFD2 (4.10)

VUT ＝ 6.2 V ＋ 0.6 V ＝ 6.8 V

VLT ＝ － 6.2 V － 0.6 V ＝ － 6.8 V

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4.3 Voltage-Controlled Oscillator

t ＝ C1 × Δ VC1

I(4.12)

0.001 μF × 13.6 V50 μA

t+1 ＝ ＝ 272μs, and

0.001 μF × 13.6 V250 μA

t+5 ＝ ＝ 54.4μs

4.3.2• Numerical Analysis

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4.3 Voltage-Controlled Oscillator

4.3.2• Numerical Analysis

fo ＝2R1C1(VUT － VLT)

＋ VIN(4.14)

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4.3 Voltage-Controlled Oscillator

4.3.3• Practical Design Techniques

1. Input voltage range 0 to 6 volts DC

2.Ramp output voltage ±4 volts (±3 volts minimum)

3.Frequency range 0 to 5.0 kHz

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4.3 Voltage-Controlled Oscillator

4.3.3• Select the Zener Diodes.

VD1 ＝ － VRAMP ＋ 0.6

VD2 ＝ ＋ VRAMP － 0.6

(4.15)

(4.16)

VD1 ＝ － 4 V ＋ 0.6 V ＝ － 3.3V, and

VD2 ＝ ＋ 4 V － 0.6 V ＝ ＋ 3.3V

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4.3 Voltage-Controlled Oscillator

4.3.3• Compute R1 and C1.

R1C1 ＝ (4.19)VIN (max)

2fHIVRAMP

＝2 × 5 kHz × 8 V

6 V

＝ 75 μs

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4.3 Voltage-Controlled Oscillator

4.3.3• Select the Op Amp.

slew rate ＝ 40fMAX[ ＋ VSAT － ( － VSAT)] (4.21)

＝40 × 5 kHz[ ＋ 13 V － ( － 13 V)]

＝ 5.2 V/μs

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4.3 Voltage-Controlled Oscillator

R3

R1

R2

V1

Vb

V2

VCC

-VCC

V3

R

C

V4 I

4.3.1( 課外補充 )• Operation

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4.3 Voltage-Controlled Oscillator

R3

R1

R2

V1

Vb

V2

VCC

-VCC

V3

R

C

V4

A

I

A ：反向觸發史密特觸發器

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4.3 Voltage-Controlled Oscillator

R3

R1

R2

V1

Vb

V2

VCC

-VCC

V3

R

C

V4

B

I

B ：數位式控制開關

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4.3 Voltage-Controlled Oscillator

R3

R1

R2

V1

Vb

V2

VCC

-VCC

V3

R

C

V4

C

I

C ：電壓隨偶器

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4.3 Voltage-Controlled Oscillator

R3

R1

R2

V1

Vb

V2

VCC

-VCC

V3

R

C

V4

D

I

D ：反向米勒積分器

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4.3 Voltage-Controlled Oscillator Analysis

1. 設輸出 V1 為正值， V1= ＋ L ， V3 = V2 = － VCC ， V4 線性增加，到＝ V4 ＋ L ×

R2

R1 + R2

，觸發電壓 V1 轉換， V1 則 = － L

2. 設輸出 V1 為負值， V1= － L ， V3 = V2 = VCC ， V4 線性減少，到＝ V4 － L ×

R2

R1 + R2

，觸發電壓 V1 轉換， V1 則 = ＋ L

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4.3 Voltage-Controlled Oscillator Output wave

Vmax

Vmin

＋ L

－ L

t

V

V1

T1 T2

V4

T1 期間斜率為 ， T2 期間斜率為VCC

RC

－ VCC

RC

= 1.Vmin － L ×R2

R1 + R2

= Vmax L ×R2

R1 + R2

2.Vmin = VCC

RC＋ × T1 Vmax

T1 = (R1 + R2)VCC

2RCR2L ， T1 = T2

3. f = T1 + T2

1= 4RCR1Vo

R1 + R2 VCC

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Thank you for your attention