J308 데이터 시트보기 (PDF) - ON Semiconductor

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J308

JFET VHF/UHF Amplifiers

ON Semiconductor 

J308

C1

INPUT L1

RS = 50 Ω

C2

L2

VS

S

G

C3

U310

D

C4

C6

BW (3 dB) − 36.5 MHz

ID − 10 mAdc

VDS − 20 Vdc

L3 OUTPUT Device case grounded

RL = 50 Ω IM test tones − f1 = 449.5 MHz, f2 = 450.5 MHz

C5

C1 = 1−10 pF Johanson Air variable trimmer.

C2, C5 = 100 pF feed thru button capacitor.

L4

C3, C4, C6 = 0.5−6 pF Johanson Air variable trim-

mer.

SHIELD

VD

L1 = 1/8″ x 1/32″ x 1−5/8″ copper bar.

L2, L4 = Ferroxcube Vk200 choke.

L3 = 1/8″ x 1/32″ x 1−7/8″ copper bar.

Figure 12. 450 MHz IMD Evaluation Amplifier

Amplifier power gain and IMD products are a function of the load impedance. For the amplifier design shown above with

C4 and C6 adjusted to reflect a load to the drain resulting in a nominal power gain of 9 dB, the 3rd order intercept point (IP)

value is 29 dBm. Adjusting C4, C6 to provide larger load values will result in higher gain, smaller bandwidth and lower IP

values. For example, a nominal gain of 13 dB can be achieved with an intercept point of 19 dBm.

+40

U310 JFET

+20 VDS = 20 Vdc

ID = 10 mAdc

0 F1 = 449.5 MHz

F2 = 450.5 MHz

−20

3RD ORDER INTERCEPT POINT

FUNDAMENTAL OUTPUT

−40

−60

−80

3RD ORDER IMD OUTPUT

−100

−120

−120 −100 −80 −60 −40 −20

0

+20

INPUT POWER PER TONE (dBm)

Example of intercept point plot use:

Assume two in−band signals of −20 dBm at the amplifi-

er input. They will result in a 3rd order IMD signal at

the output of −90 dBm. Also, each signal level at the

output will be −11 dBm, showing an amplifier gain of

9.0 dB and an intermodulation ratio (IMR) capability

of 79 dB. The gain and IMR values apply only for sig-

nal levels below comparison.

Figure 13. Two Tone 3rd Order Intercept Point

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