J308 J309 J310

5

Motorola Small–Signal Transistors, FETs and Diodes Device Data

Figure 12. 450 MHz IMD Evaluation Amplifier

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.

INPUT

RS = 50 Ω

C1

C2

L1

L2

VS

S

G

D

SHIELD

C3

U310

C4

VD

L3

C5

L4

C6

OUTPUT

RL = 50 Ω

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.

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

–20

–40

–60

–80

–100

–120

–120

+20

–100

–80

–60

INPUT POWER PER TONE (dBm)

0

+20

+40

–40

–20

0

3RD ORDER INTERCEPT POINT

FUNDAMENTAL OUTPUT

3RD ORDER IMD OUTPUT

U310 JFET

VDS = 20 Vdc

ID = 10 mAdc

F1 = 449.5 MHz

F2 = 450.5 MHz