Mathcad - ee217projtodonew2.mcd

A 3 N, I C
, Z S
, s 1
, s 2
, s 3 A 1 N, I C
, Z S , s 1 s 2 s 3
A 3 N, I C
, 50 ohm, s 1
, s 2
, s 3 8.458 5.157i mA
V 3
V
. T . A
3 1 N, I C
, Z S
, s . 1
A 1 N, I C
, Z S
, s . 2 A 1 N, I C
, Z S
, s 3
3I . C + 3I . . C A1A2 N , I C , Z S , s 1 , s 2 , s 3
= Third Order Distortion Term
Z in N, I C
, s r b ( N) Z π N, I C
, s 1 g m I . C Z π N, I C
, s Z e ( N,
s)
. Input Impedance
Z in N, I C
, s = 463.053 21.963i ohm
IP 3 N, I C , Z S , f, ∆f s j. 2. π . f
∆s j. 2. π . ∆f
10.
log
IP 3 N, I C , Z S N, I C , s , f, ∆f 12.046 dB
1 4 A
. 1 N, I C , Z S , s
. . 1 . 1
1mW3
A 3 N, I C , Z S , s, s,
( s ∆s)
8 50 ohm
= Third Order Intercept Point
20
16
Intercept Point (dBm)
10
0
3rd Order Intercept Point (dBm)
14
12
10
10
0 5 10 15 20
8
0 20 40 60 80 100
Bias Current (mA)
3rd Order Intercept Point (dBm)
Number of Devices in Parallel
Third Order Intercept Point (dBm)
Fig. 31: IP3 vs. Bias Current
Fig. 32: IP3 vs. Device Size
It is interesting to understand the shape of the 3 rd order intercept point curve as a function of
device size. For small device sizes, as the device size is increased the distortion performance gets
worse, but for very large devices the distortion performance gets better as the device size
increases. This fact is not explained with the simplified equations for the distortion given above.
The simplified equations for distortion given above neglect the resistance of the emitter as a
function of device size. The shape can be described better by separating the interept point into it’s
two components: The linear term, A 1 , and the nonlinear term, A 3 . As we plot A 1 and A 3 as a
function of device size, we notice A 3 is a much stronger function of area than A 1 , but they both
have a similar shape. The intercept point reaches it’s minimum about the same time A 1 reaches it’s
maximum.