J308 Datasheet, PDF (5/8 Pages) ON Semiconductor – JFET VHF/UHF Amplifiers

C1
INPUT ^L1
RS = 50 Ω
C2
L2
VS
S
G
C3
U310
D
C4
SHIELD
C6
L3 _OUTPUT
RL = 50 Ω
C5
L4
VD
J308 J309 J310
BW (3 dB) – 36.5 MHz
ID – 10 mAdc
VDS – 20 Vdc
Device case grounded
IM test tones – f1 = 449.5 MHz, f2 = 450.5 MHz
C1 = 1–10 pF Johanson Air variable trimmer.
C2, C5 = 100 pF feed thru button capacitor.
C3, C4, C6 = 0.5–6 pF Johanson Air variable
trimmer.
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 amplifier 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 signal levels below comparison.
Figure 13. Two Tone 3rd Order Intercept Point
Motorola Small–Signal Transistors, FETs and Diodes Device Data
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