參數(shù)資料
型號: ZN428J-8
元件分類: 參考電壓二極管
英文描述: Low Current Operation at 250 ,Low Reverse Leakage,Low Noise Zener Diode
中文描述: 250 的低電流運算,低反向泄露,低噪聲穩(wěn)壓二極管
文件頁數(shù): 8/9頁
文件大小: 272K
代理商: ZN428J-8
ZN428
(2) Bipolar D-A Converter
For bipolar operation the output from the ZN428 is offset
by half full-scale by connecting a resistor R3 between V
REF
IN
and the inverting input of the buffer amplifier (Fig.9).
When the digital input to the ZN428 is zero the analog
output is zero and the amplifier output should be -Full-scale.
An input of all ones to the D-A will give a ZN428 output of
V
REF IN
and the amplifier output required is +Full-scale. Also,
to match the ladder resistance the parallel combination of
R
1
, R
2
and R
3
should be 4k
.
The nominal values of R
1
, R
2
and R
3
which meet these
conditions are given by
R
1
= 8Gk
, R
2
= 8G/(G-1)k
and R
3
= 8k
.
where the resultant output range is
±
G V
REF IN
. A bipolar
output range of
±
V
REF IN
(which corresponds to the basic
unipolar range 0 to V
REF IN
) is obtained if R
1
= R
3
= 8k
and
R
2
=
.
Assuming that V
REF IN
= 2.5V the nominal values of
resistors for
±
5 and
±
10V output ranges are given in the
following table:
Minus full scale (0ffset) is set by adjusting R
1
about its
nominal value relative to R
3
. Plus full-scale (gain) is set by
adjusting R
2
relative to R
1
.
Practical circuit realisations are given in Fig.10.
Note that in the
±
5V case R
3
has been chosen as 7.5k
(instead of 8.2k
) to get a more symmetrical range of
adjustment using standard potentiometers. Settling time for a
major transition is 1.5
μ
s typical.
Output Range
G
R
1
R
2
R
3
+5V
2
16k
16k
8k
+10V
4
32k
10.66k
8k
UNIPOLAR ADJUSTMENT PROCEDURE
(i) Set all bits to OFF (low) with ENABLE low and adjust
zero until V
OUT
= 0.0000V.
(ii) Set all bits ON (high) and adjust gain until V
OUT
= FS
- 1LSB.
UNIPOLAR SETTING UP POINTS
1LSB = FS
256
Output Range, +FS
LSB
FS - 1LSB
+5V
19.5 mV
4.9805V
+10V
39.1mV
9.9609V
UNIPOLAR LOGIC CODING
Input Code
(Binary)
Analog Output
(Nominal Value)
11111111
11111110
11000000
10000001
10000000
01111111
01000000
00000001
00000000
FS - 1LSB
FS - 2 LSB
3
/
4
FS
1
/
2
FS + 1LSB
1
/
2
FS
1
/
2
FS - 1LSB
1
/
4
FS
1LSB
0
Fig.9 Bipolar operation - basic circuit
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