Investigation of HPM Effects in Voltage Controlled Oscillators

Dr. John Rodgers and Cristina AllenUniversity of Maryland

Mid Progress ReportJuly, 2010

Submitted to Dr. Bill ZimmermanVoss Scientific

ZX95-988 VCO Characteristics

-1.00 -0.86 -0.72 -0.58 -0.44 -0.30 -0.16 -0.02-0.1

-0.08

-0.06

-0.04

-0.02

6.93889390390723E-17

0.0200000000000001

Tuning Voltage (V)

Curr

ent (

A)

I-V Curve (Diode-Like)

-0.5 -0.1 0.3 0.7 1.1 1.5 1.9 2.3 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 5.9800

850

900

950

1000

1050

1100

Tuning Voltage (V)

Freq

uenc

y (M

Hz)

VCO Tuning Curve

Slope = 26.29 MHz/V

ZX95-988 VCO Characteristics

893.148481 893.217147666675 893.28581433335-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

Normal VCO Output Spectrum (Vtune = 0)

Frequency (MHz)

Spec

tral

Pow

er (d

Bm)

-0.5 -0.136666675331071 0.226666649337858-18-16-14-12-10

-8-6-4-20

VCO Phase Noise Line Width (3dB)~ 50 Hz

893.2 MHz + Delta F (kHz)Sp

ectr

al P

ower

(dBm

)

VCO Experiment

Bias T

VCORF Oscillator(Pulse Modulated)

25 GSa/sDigitizer

TuningInput

RFOutput

DC Bias

5 VDC

•The nonlinear I-V characteristic of the tuning input provided evidence that this port may be unstable under pulsed RF excitation.•We characterized the VCO operation when the tuning voltage consists of an RF pulse superimposed on a DC bias.

1. A wideband bias tee was utilized to combine the DC and RF signals.2. The RF amplitude was stepped in 50 mV increments from 50 –

1000mV. The pulse width was fixed at 100 ms. Carrier frequencies 500 < f < 4000 MHz were investigated.

3. The VCO output waveform was digitized and recorded for each frequency and amplitude step. Subsequently, the FFT of the time-domain signal was calculated to give the RF spectrum.

4. Composite spectrograms were constructed to analyze how the VCO output varied with excitation parameters.

Results when RF was injected at frequencies near the VCO fundamental showing a frequency pulling and

broadening effect(Representative Spectrograms)

Freq 887MHz / Vt 0V

RF Voltage (V)

Fre

quen

cy (

MH

z)

100 200 300 400 500 600 700 800 900 1000

893

893.2

893.4

893.6

893.8

894

Freq 903MHz / Vt 0V

RF Voltage (V)

Fre

quen

cy (

MH

z)

100 200 300 400 500 600 700 800 900 1000893.2

893.4

893.6

893.8

894

894.2

894.4

894.6

Injected Carrier f = 887 MHz

Note: Normal VCO output frequency for Vtune = 0 is approximately 893.8MHz

Injected Carrier f = 903 MHz

More examples of effects when injected frequency is close to VCO fundamental frequency

Freq 891MHz / Vt 0V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000891

891.5

892

892.5

893

893.5

894Freq 893MHz / Vt 0V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000893

893.2

893.4

893.6

893.8

894

894.2

894.4

Freq 895MHz / Vt 0V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000893.2

893.4

893.6

893.8

894

894.2

894.4

894.6

894.8

895

895.2Freq 897MHz / Vt 0V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000

893

893.5

894

894.5

895

895.5

896

896.5

897

Phase Locking

Phase Locking

Spectral Broadening

Results with RF near the second harmonic of the VCO fundamental (1.784-1.804GHz)

Freq 1798MHz / Vt 0V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000892.6

892.8

893

893.2

893.4

893.6

893.8

894

894.2

894.4

894.6

Freq 1788MHz / Vt 0V

RF Voltage (V)

Fre

quen

cy (

MH

z)

100 200 300 400 500 600 700 800 900 1000

893.3

893.4

893.5

893.6

893.7

893.8

893.9

894

894.1

Results with RF near the third harmonic of the VCO fundamental frequency (2.681-2.701GHz)

Freq 2691MHz / Vt 0V

RF Voltage (V)

Fre

quen

cy (

MH

z)

100 200 300 400 500 600 700 800 900 1000893.5

893.6

893.7

893.8

893.9

894

894.1

894.2

894.3

Freq 2701MHz / Vt 0V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000893

893.5

894

894.5

895

Freq 2681MHz / Vt 0V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000893.2

893.4

893.6

893.8

894

894.2

894.4

894.6

Freq 2746MHz / Vt 0.5V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000

914.4

914.6

914.8

915

915.2

915.4

915.6

915.8

Supplemental Data

• The following series of slides shows examples of the results for various tuning voltages and injection frequencies:

Fundamental Frequency Range(908-928MHz)

Note: Average VCO output for Vtune = 0.5V is 915.2MHz

Freq 924MHz / Vt 0.5V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000915

915.05

915.1

915.15

915.2

915.25

915.3

915.35

915.4

915.45

Fundamental Frequency Injection(908-928 MHz)

Behavior when injected frequency is close to VCO output frequency @ Vt = 0.5VFreq 912MHz / Vt 0.5V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000912

912.5

913

913.5

914

914.5

915

915.5Freq 914MHz / Vt 0.5V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000

914

914.5

915

915.5

916

Freq 916MHz / Vt 0.5V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000914.4

914.6

914.8

915

915.2

915.4

915.6

915.8

916

916.2Freq 918MHz / Vt 0.5V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000915

915.5

916

916.5

917

917.5

918

Second Harmonic Frequency(1.826-1.846GHz)

Freq 1828MHz / Vt 0.5V

RF Voltage (V)

Fre

quen

cy (

MH

z)

100 200 300 400 500 600 700 800 900 1000914.95

915

915.05

915.1

915.15

915.2

915.25

915.3

915.35

915.4

915.45Freq 1840MHz / Vt 0.5V

RF Voltage (V)

Fre

quen

cy (

MH

z)

100 200 300 400 500 600 700 800 900 1000914.8

914.9

915

915.1

915.2

915.3

915.4

915.5

915.6

915.7

Representative of 1.826,1.828, and 1.832GHz

Representative of 1.836-1.846GHz

Second Harmonic Frequency(1.826-1.846GHz)

Only plot that deviated from representative plot. Injected frequency is the second harmonic of VCO output.

Freq 1830MHz / Vt 0.5V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000914.8

914.9

915

915.1

915.2

915.3

915.4

Third Harmonic Range(2.744-2.764GHz)

Freq 2754MHz / Vt 0.5V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000

914.4

914.6

914.8

915

915.2

915.4

915.6

915.8

Fundamental Frequency (925-945MHz)

Freq 927MHz / Vt 1V

RF Voltage (V)

Fre

quen

cy (

MH

z)

100 200 300 400 500 600 700 800 900 1000932.5

932.55

932.6

932.65

932.7

932.75

932.8

932.85

932.9

932.95

933Freq 939MHz / Vt 1V

RF Voltage (V)

Fre

quen

cy (

MH

z)

100 200 300 400 500 600 700 800 900 1000932.2

932.3

932.4

932.5

932.6

932.7

932.8

932.9

933

933.1

933.2

Representative of 925-925MHz Representative of 935-945MHz

Note: VCO frequency for Vt = 1.0V is 932.75MHz

Vt = 1.0 V

Behavior when injected frequency is close to VCO output frequencyFreq 931MHz / Vt 1V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000931

931.2

931.4

931.6

931.8

932

932.2

932.4

932.6

932.8

933Freq 933MHz / Vt 1V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000932.4

932.5

932.6

932.7

932.8

932.9

933

933.1

933.2

933.3

Freq 935MHz / Vt 1V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000932.5

933

933.5

934

934.5

935

Second Harmonic Frequency(1.860-1.880GHz)

Only plot that deviated from representative plot. Injected frequency is double VCO output frequency (actual second harmonic of VCO output).

Freq 1866MHz / Vt 1V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000932.2

932.3

932.4

932.5

932.6

932.7

932.8

932.9

933

933.1

933.2

Third Harmonic Frequency(2.795-2.815GHz)

Freq 2805MHz / Vt 1V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000931.5

932

932.5

933

933.5

934

Third Harmonic Frequency(2.795-2.815GHz)

Only plot that deviated from representative plot. Injected frequency is third VCO output frequency (actual third harmonic of VCO output).

Freq 2799MHz / Vt 1V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000931.5

932

932.5

933

933.5

934

Third Harmonic Frequency(2.795-2.815GHz)

This plot had the overall shape of the representative plot, but showed a the highest spectral broadening.

Freq 2801MHz / Vt 1V

RF Voltage (V)

Fre

quency (

MH

z)

100 200 300 400 500 600 700 800 900 1000931.5

932

932.5

933

933.5

934

Conclusions• RF coupled into the diode at the tuning voltage input drives

the P-N junction into nonlinearity. This process generates spurious voltages which produce unstable VCO operation.

• The VCO is particularly sensitive to RF pulses when the carrier frequency is near harmonics of the VCO output.

• In the most sensitive cases, RF pulse amplitudes as low as 100 mV were enough to drive instability in the VCO.

• The effects observed in the experiments can be categorized generally as follows:1. Spectral broadening2. Phase locking of the VCO to the RF carrier frequency3. Generation of nonlinear frequency products

Current and Near-Future Efforts

• We are now developing nonlinear circuit models based on the results of the data presented here.

• Initially, we will model direct injection of RF into the tuning voltage input and compare the numerical and experimental results. This will provide initial validation of the circuit models.

• The VCO circuit will be tested in the UMD radiation chamber where the RF coupling, transmission and effects will be characterized.

• Finally, the results of the chamber tests will be compared with simulations using a combination of the deterministic circuit effects models and the Voss coupling models.