參數(shù)資料
型號: MAT02EHZ
廠商: ANALOG DEVICES INC
元件分類: 小信號晶體管
英文描述: 20 mA, 40 V, 2 CHANNEL, NPN, Si, SMALL SIGNAL TRANSISTOR, TO-78
封裝: METAL CAN-6
文件頁數(shù): 10/12頁
文件大?。?/td> 260K
代理商: MAT02EHZ
OBSOLETE
MAT02
–7–
REV. E
Figure 3. One-Quadrant Multiplier/Divider
APPLICATIONS: NONLINEAR FUNCTIONS
MULTIPLIER/DIVIDER CIRCUIT
The excellent log conformity of the MAT02 over a very wide
range of collector current makes it ideal for use in log-antilog
circuits. Such nonlinear functions as multiplying, dividing,
squaring and square-rooting are accurately and easily imple-
mented with a log antilog circuit using two MAT02 pairs (see
Figure 3). The transistor circuit accepts three input currents (I1,
I2 and I3) and provides an output current IO according to
IO = I1I2/I3. All four currents must be positive in the log antilog
circuit, but negative input voltages can be easily accommodated
by various offsetting techniques. Protective diodes across each
base-to-emitter junction would normally be needed, but these
diodes are built into the MAT02. External protection diodes
are, therefore, not needed.
For the circuit shown in Figure 3, the operational amplifiers
make I1 = VX/R1, I2 = VY/R2, I3 = VZ/R3, and IO = VO/RO. The
output voltage for this one-quadrant, log-antilog multiplier/
divider is ideally:
VO =
R3RO
R1R2
V XVY
V Z
(VX, VY, VZ > 0)
(4)
If all the resistors (RO, R1, R2, R3) are made equal, then
VO = VXVY/VZ
Resistor values of 50 k
to 100 k are recommended assuming
an input range of 0.1 V to +10 V.
ERROR ANALYSIS
The base-to-emitter voltage of the MAT02 in its forward active
operation is:
VBE =
kT
q
In
IC
IS
+ rBEIC, VCB ~ 0
(5)
The first term comes from the idealized intrinsic transistor
equation previously discussed (see equation (1)).
Extrinsic resistive terms and the early effect cause departure
from the ideal logarithmic relationship. For small VCB, all of
these effects can be lumped together as a total effective bulk
resistance rBE. The rBEIC term causes departure from the desired
logarithmic relationship. The rBE term for the MAT02 is less
than 0.5
and rBE between the two sides is negligible.
Returning to the multiplier/divider circuit of Figure 1 and using
Equation (4):
VBE1A + VBE2A – VBE2B – VBE1B + (I1 + I2 – IO – I3) rBE = 0
If the transistor pairs are held to the same temperature, then:
kT
q
In
II
kT
q
In
II
O
S ASA
SB S B
12
3
12
=
+ (I1 + I2 – IO – I3) rBE (6)
If all the terms on the right-hand side were zero, then In
(I1 I2/I3 IO) would equal zero, which would lead directly to
the desired result:
IO =
I1I2
I3
, where I1, I2, I3, IO > 0
(7)
Note that this relationship is temperature independent. The
right-hand side of Equation (6) is near zero and the output
current IO will be approximately I1 I2/I3. To estimate error,
define as the right-hand side terms of Equation (6):
= In
II
q
kT
S ASA
SB S B
12
+
(I1 + I2 – IO – I3) rBE
(8)
For the MAT02, In (ISA/ISB) and ICrBE are very small. For small
,
ε ~ 1 + and therefore:
I1I2
I3IO
= 1 +
(9)
IO ~
I1I2
I3
(1 – )
The In (ISA/ISB) terms in cause a fixed gain error of less than
±0.6% from each pair when using the MAT02, and this gain
error is easily trimmed out by varying RO. The IOUT terms are
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