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參數(shù)資料
| 型號(hào)： | TC835CPI |
| 廠商： | TelCom Semiconductor, Inc. |
| 英文描述： | PERSONAL COMPUTER DATA ACQUISITION A/D CONVERTER |
| 中文描述： | 個(gè)人計(jì)算機(jī)數(shù)據(jù)采集的A / D轉(zhuǎn)換器 |
| 文件頁(yè)數(shù)： | 5/12頁(yè) |
| 文件大?。?/td> | 206K |
| 代理商： | TC835CPI |
3-69
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
+
–
+
–
+
–
+IN
IN
REF
ANALOG
–IN
SWI
SWR
SWZ
SWI
SW1
SWZ
SWIZ
SWZ
INTEGRATOR
SWITCH CLOSED
SWITCH OPEN
SWRI
+
SWRI
–
COMPARATOR
TO
SWRI
+
SWRI
–
INANALOG
RINT
CINT
CREF
CSZ
Figure 3E. Integrator Output Zero Phase
GENERAL THEORY OF OPERATION
(All Pin Designations Refer to 28-Pin DIP)
Dual-Slope Conversion Principles
The TC835 is a dual-slope, integrating analog-to-digital
converter. An understanding of the dual-slope conversion
technique will aid in following the detailed TC835 opera-
tional theory.
The conventional dual-slope converter measurement
cycle has two distinct phases:
(1) Input signal integration
(2) Reference voltage integration (deintegration)
The input signal being converted is integrated for a fixed
time period. Time is measured by counting clock pulses. An
opposite polarity constant reference voltage is then inte-
grated until the integrator output voltage returns to zero. The
reference integration time is directly proportional to the input
signal.
In a simple dual-slope converter, a complete conversion
requires the integrator output to "ramp-up" and "ramp-
down."
A simple mathematical equation relates the input signal,
reference voltage, and integration time:
∫
0
RC
The dual-slope converter accuracy is unrelated to the
integrating resistor and capacitor values, as long as they are
stable during a measurement cycle. An inherent benefit is
noise immunity. Noise spikes are integrated, or averaged, to
zero during the integration periods. Integrating ADCs are
immune to the large conversion errors that plague succes-
sive approximation converters in high-noise environments.
(See Figure 4.)
TC835 Operational Theory
The TC835 incorporates a system zero phase and
integrator output voltage zero phase to the normal two-
phase dual-slope measurement cycle. Reduced system
errors, fewer calibration steps, and a shorter overrange
recovery time result.
The TC835 measurement cycle contains four phases:
(1) System zero
(2) Analog input signal integration
(3) Reference voltage integration
(4) Integrator output zero
Internal analog gate status for each phase is shown in
Table 1.
+
–
REF
VOLTAGE
ANALOG
INPUT
SIGNAL
+
–
DISPLAY
SWITCH
DRIVER
CONTROL
LOGIC
I
O
CLOCK
COUNTER
POLARITY CONTROL
PHASE
CONTROL
VIN
VIN
VFULL SCALE
1/2 VFULL SCALE
VARIABLE
REFERENCE
INTEGRATE
TIME
FIXED
SIGNAL
INTEGRATE
TIME
INTEGRATOR
COMPARATOR
'
'
Figure 4. Basic Dual-Slope Converter
where:
V
R
= Reference voltage
t
SI
= Signal integration time (fixed)
t
RI
= Reference voltage integration time (variable).
For a constant V
:
.
]
[
t
SI
V
IN
(t) dt =
1
V
R
t
RI ,
RC
V
IN
= V
R
t
RI
t
SI
TC835
PERSONAL COMPUTER
DATA ACQUISITION A/D CONVERTER
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