U308, U309, U310
FIGURE 12 - 450 MHz IMD EVALUATION AMPLIFIER
wB (3dB) - 36.5 MHz
V DS 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 trim
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.
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.
FIGURE 13 - TWO TONE 3RD ORDER INTERCEPT POINT
+20 VQS-20 Vd
lfj = 10 mAdc
__RDC RDE R IN" ERC EPTP DINT
F1 = 44i ,5MHz
F2 = 46( .5 MHz
FUNDAM ENT^\L0L TPU
t/3RD 0R[ ER I I/ID0 JTPU
-80 -60 -40 -21
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 - 1 1 dBm, show-
ing 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 compression.