Cypress CY8CKIT-025, Руководство пользователя

Страница: 28 / 86

CY8CKIT-025 PSoC® Precision Analog Temperature Sensor Expansion Board Kit Guide, Doc. # 001-65791 Rev. *J 28
Hardware
4.5 Diode
Application note AN60590 - PSoC 3 and PSoC 5LP Temperature Measurement using Diode
explains the theory behind diode temperature measurement. This section provides only a short
description of the method. The current through a forward-biased diode is given by the equation:
Equation 7
where,
V
is the diode forward voltage drop
I
S
is the reverse saturation current

is the constant that has a value between 1 and 2, depending on the material and physical structure
of the diode
V
T
is the thermal voltage calculated with the equation
where,
k
is the Boltzmann's constant
T
is the absolute temperature in Kelvin
q
is the magnitude of electron charge
By passing two currents
I
1
and
I
2
and measuring the respective voltages
V
1
and
V
2
, the temperature
can be calculated using the following equation.
Equation 8
Figure 4-4 shows the circuit diagram used for diode temperature measurement. Note that two diodes
are connected antiparallel to each other. This helps to measure two temperatures using only four
pins.







T
s
V
v
EXP I I

q
kT
V
T
