http://www.hfoscillators.com/apskhanna/articles/IMS1987Fast

Q-9 FAST-SETTLING

,

LOW

NOISE

Ku

BAND

FUNDAMENTAL

BIPOLAR

VCO

A.P.S.KHANNA Amplifier

and

Source AVANTEK,

3175 Bowers Santa ClararCA.

Products

approach for realization first Ku-band

ABSTRACT:

This paper discusses fast-settling fundamental-output voltagecontrolled oscillators in the Ku Band (15 to 18 GHz & 12 to 15 GHz), using silicon bipolar transistors and silicon varactor diodes.

With these oscillators the output frequency settles within 2 AS to within ~1 MHz of the final frequency.

Phase noise at 16.2 GHz was measured to be -93 dBc/Hz at 100 kHz from the carrier.

INTRODUCTION

will

:

discuss design

CHARACTERIZATION:

active device used The for the oscillator is an Avantek-developed interdigitated arsenic-emitter Si bipolar transistor with 0.5 yn emitter 2 pm width and emitter-emitter pitch[3].

This device has 20 emitters with an emitter length of 15 pm, and a of higher than 30 GHz. measured Fmax When biased at 10V, 20 mA the Ft and Fs (S21=OdB) were both approximately 10 4 GHz was 16.7 dB and MUG GHz . MAG at at 18 GHz was 6 dB. For tuning, a silicon abrupt varactor diode developed

by Avantek was selected for its high-Q performance compared to commercially-available silicon abrupt 5000 diodes.

With this diode, a Q of was

measured

capacitance

at ratio

50 of

4.2

MHz,

with

from

1

a to

20

v.

OSCILLATOR

DESIGN

APPROACH:

configuration was A common-collector selected due to its inherent instability, minimum parasitic in the circuit layout, and wider resulting bandwidth capability compared to common-base or common-emitter circuits.

Figure 1 shows the oscillator circuit.

The parallel compensating reactance shown in Fig. 2 is used to increase the oscillator bandwidth of a VCO[41.

It may be noted that the compensating will be inductive or reactance capacitive depending on the sign of the oscillator input admittance of device.

Figure 2 shows the principle of compensating the operation of Using the small signal reactance. the resistance approach, negative analysis was done looking into the base the with capacitive of device , reactance on the emitter

A recently-develope d highperformance silicon bipolar has made it transistor[3] now possible to realize bipolar VCOS with fundamental outputs of up to 18 GHz. using a silicon-silicon technology, i.e. a silicon bipolar transistor and silicon a abrupt varactor diode, low-noise VCOS have fast-settling, been realized covering 12 to 15 GHz and 15 to 18 GHz. paper we characterization,

the VCO design, practical and measurement of the fundamental bipolar VCO.-

DEVICE

Voltage Controlled Oscillators have been a key element for electronic warfare systems because of their fast switching, low power consumption and size.

Until now Ku-band small fundamental VCOS have only been built using GaAs FETs[l].

It is well known that a GaAs FET oscillator is not only noisier, but also poorer in terms of switching time than a silicon bipolar transistor oscillator.

Bipolar transistors have been used in push-push ( second harmonic) configurations in Ku band such circuits have VCOS[2].

However, a number such as of disadvantages, spurious outputs at the fundamental frequency, the increased number of devices required and the complexity of the circuit compared to a fundamental oscillator.

In this device

Division

INC. Ave. 95054

the

579 0149-645X8710000-0579$01

.00

0

1987 IEEE

1987 IEEE

M’lTS

Digest

The

terminal. feedback

and

optimized resistance bands to

to in of

GHz .

12

capacitive

the

bias

generate the desired to

15

GHz

Computer-aided

analyze

the

presents

series

circuits the and

15 was

to

18

circuit.

power for

Parameter

Low

Freq.Band

12

Min.

Ku

output

the

vs.

hiqh-band

Band 15

GHz

+6dBm

2:1

14

MHz

Freq.

Drift -54 to 750C

<

240

MHZ

2n

<

-15

dBc

Harmonic

Parameter

High

Freq.Band

15

Min.

Ku to

Power

Pulling

REALIZATION:

to

Power

Pulling

The circuit discussed above was realized on a alumina 10 mil substrate.

The bipolar transistor was operated at a bias of 9 Volts Vce and Ie=16 mA. The capacitance required in the emitter circuit was realized using microstrip distributed capacitance, and the bias circuits were designed to cover the complete Ku band, without deteriorating the settling time performance of the oscillator.

The abrupt varactor is an Avantek-developed diode with a Cj(4) of 0.5 pf.

A reference voltage of -9 volt was used on the tuning diode, necessitating a bipolar tuning voltage.

To optimize the complete oscillator for practical output power, while maintaining bandwidth, a single-stage Ku-band FET amplifier is GaAs provided at the oscillator output.

The amplifier stage uses a proprietary Avantek 0.5-~ GaAs FET, biased at 30 mA, with Vds adjusted to 4.5 volts.

Band

18

GHz

+3 dBm

2:1

20

MHz

Freq.

Drift -54 to 750C

<

355

MHZ

2nd

<

-15

dBc

Harmonic

Modulation

Sensitivity

& settling

time:

Modulation sensitivity over the band varied from 50MHz/V to 250MHz/v.

The settling time was measured using the frequency counter method, and the downconverted frequency discriminator method.

The oscillator frequency settling within +1 MHz was measured to be less than 2 ps as shown in fig.4 Phase

Noise:

Oscillator phase noise using the delay line technique.

The results fig.

5, indicating a 93 dBc at 100 kHz from GHz .

was measured discriminator are shown in phase noise ofcarrier at 16.2

ACKNOWLEDGEMENT The

OSCILLATOR

detected voltage

used

Next, the varactor circuit and the output circuit were modeled, combined into the oscillator circuit model, and optimized to achieve oscillation Oscillation in the desired bands. conditions[5] were analyzed using small signal S-parameter analysis.

The output matching circuit is very lightly coupled in order to achieve that the low noise and to assure device will oscillate at the highest frequency possible.

Although lighter coupling results in lower output power, it makes it possible to achieve higher frequency oscillations and wide bandwidth over the desired operating temperature range.

PRACTICAL

the tuning

oscillator-.

negative frequency

design oscillator

the

were

author

is

for fruitful for his fabrication

PERFORMANCE:

Two oscillators were required in order to cover the entire Ku band, the low-band oscillator tuning from 12 to 15 GHz and the high-band oscillator 15 to 18 GHz. Basic parameters of both the oscillators are given in the table below.

Fig. 3

oscillators. the work

the design transistor respectively.

580

of

thankful

: to

Bob

Oyafuso

discussions and Jack Huynh craftsmanship in the and testing of the The author acknowledges C. LeUng and R. Curby for

and

of silicon silicon varactor

bipolar diode

REFERENCES:

1.

and J. Kaminisky, A. Bert Ku Band Voltage “Wideband Oscillators”, Controlled European Microwave Conference 1986.

Proc.

— ~ Berlin

~ -B(w)

Winch.

“Verv Broadband R. G. Vc’o” , E-lectronics Bipolar Nov. VO1.17 NO.23, Letters~ 1981, pp.

871-873.

2.

/ 1,

II

/,1

c.

c.

Leung, C. P. Snapp and V. “A 0.5 ~ silicon bipolar Grande, transistor for low phase noise applications up to 20 GHz”, IEEE Jun. Di g est , MTT-S Int. Sym 1985, pp.

383-38;.

3.

-G(w)

P. Marechal and J. Obregon, “1.5 tuned to4.5 varactor European Microwave oscillators”, EMC Proceedings~ Conference 1979, Brighton, U.K.

4.

J. Obregon “Microwave IEEE Trans.

5.

Fig.

I

Khanna, and A.P.S. Oscillator Analysis”, MTT< June 1981.

Ku Band Bipolar

I

I

Approach

for

1

I

a

Wideband

I

1

1

t

TIME

I&l

1@p

VCO Configuration

4

Settling

RFTER

I

1

TRIGGER

for

lm

14.3 GHz to 16 GHz

-40 -60 -80

.,

-1oo I

-120 -140 -160

[

lK

IOK F(

Fig.

3

High Band Frequency

vs.

Tuning

Fig.

Voltage

581

5

Phase

Jrier Noise

1

I

i

1O@p

Time Plot

VCO

I

1 MHz PER DIVISION

4 Fig.

1

1

Design

t

D

Fig.

2

100K

Fre at

]uency

16.2

lM (Hz)

GHZ