廬
APPLICATION BULLETIN
VOLTAGE-REFERENCE FILTERS
By R. Mark Stitt (602) 746-7445
Mailing Address: PO Box 11400 鈥?Tucson, AZ 85734 鈥?Street Address: 6730 S. Tucson Blvd. 鈥?Tucson, AZ 85706
Tel: (520) 746-1111 鈥?Twx: 910-952-111 鈥?Telex: 066-6491 鈥?FAX (520) 889-1510 鈥?Immediate Product Info: (800) 548-6132
IMPROVED VOLTAGE-REFERENCE
FILTER HAS SEVERAL ADVANTAGES
q
LOW OUTPUT IMPEDANCE AT HIGH
FREQUENCY FOR DRIVING DYNAMIC LOADS
SUCH AS HIGH-SPEED A/D CONVERTERS
q
IMPROVED NOISE FILTERING
q
BETTER ACCURACY BY ELIMINATING
CAPACITOR LEAKAGE ERRORS
q
DRIVES LARGE CAPACITIVE LOADS
The Burr-Brown REF102 is a buried-zener-based precision
10.0V reference. It has better stability and about five times
lower output noise than band-gap-based voltage references
such as the PMI REF-10. Still, its output noise is about
600碌Vp-p at a noise bandwidth of 1MHz (the output noise
of the PMI REF-10 is about 3,000碌Vp-p at 1MHz).
So far as we know, the stability with time of the REF102 is
significantly better than any other single-chip voltage refer-
ence on the market. We plan more characterization of stabil-
ity vs time, but it will probably not be available this year.
The following preliminary data is all we have for now. The
devices used were off-the-shelf. They were not burned-in, or
otherwise stabilized prior to this stability test.
Noise of a voltage reference can be reduced by filtering its
output. Broadband noise can be reduced by the square-root
of the reduction in noise bandwidth. Filtering the output of
the reference to reduce the noise bandwidth by 100/1 (from
1MHz to 10kHz, for example) can reduce the noise by 10/
1 (from 600碌Vp-p to 60碌Vp-p).
The conventional circuit, shown in Figure 1, uses a single-
pole RC filter and a buffer amplifier. One problem with this
circuit is that leakage current through the filter capacitor, C
1
,
flows through R
1
resulting in DC error. Furthermore, changes
in leakage with temperature result in drift. The relatively
low RC time constants often needed dictate large capacitor
values prone to this problem.
+15V
2
V+
REF102
10V 6
Out
R
1
OPA27
+10V
OUT
Com
4
C
1
FIGURE 1. Voltage Reference with Conventional Filter.
REF102CM +10.0V REFERENCE STABILITY vs TIME
T
A
= 25擄C, V
S
= +15V.
V
OUT
CHANGE
FROM 1 HR
TO 168 HRS
[ppm]
6.8
5.1
9.4
9.6
12.9
10.5
10.3
17.0
6.2
7.1
13.0
7.5
13.0
4.2
7.3
V
OUT
CHANGE
FROM 1 HR
TO 1008 HRS
[ppm]
5.5
1.0
6.5
6.9
7.8
6.4
5.7
14.5
5.1
1.7
9.6
4.7
9.5
3.0
4.3
V
OUT
CHANGE
FROM 1 HR
TO 2016 HRS
[ppm]
7.1
1.2
3.2
7.7
9.6
5.3
6.2
12.9
3.8
1.3
9.6
3.9
10.4
0.5
2.6
V
OUT
CHANGE
FROM 1 HR
TO 3072 HRS
[ppm]
4.7
鈥?.1
1.0
5.6
6.7
3.0
3.7
9.2
1.7
0.1
10.0
4.2
8.2
鈥?.3
1.8
V
OUT
CHANGE
FROM 1 HR
TO 5136 HRS
[ppm]
8.2
0.1
1.8
7.6
9.5
5.4
5.8
9.9
2.7
1.0
13.0
5.0
9.9
4.2
4.1
V
OUT
CHANGE
FROM 1 HR
TO 14205 HRS
[ppm]
11.7
1.3
2.0
10.3
12.8
9.4
8.2
13.7
4.1
2.4
16.5
7.4
13.7
2.8
3.9
UNIT
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
漏
1990 Burr-Brown Corporation
1
AB-003A
Printed in U.S.A. March, 1991
1
2
