Maxim Integrated 71M6541 Demo Board - Manual (Page 38)

71M6541 Demo Board REV 3.0 User’s Manual
38 Rev 4.0
3a.
[ ]
1
) 60 cos(
) sin( ) 60 sin( ) cos( ) 60 cos(
60
−
+
= S S XI XV
A A
E
φ φ
1 ) sin( ) 60 tan( ) cos(
− + =
S XI XV S XI XV
A A A A
φ φ
Combining 2a and 3a:
4.
) tan( ) 60 tan( ) 1 (
0 0 60 S
E E E
φ + + =
5.
) 60 tan( ) 1 (
) tan(
0
0 60
+
−
=
E
E E
S
φ
6.  





+
−
= −
) 60 tan( ) 1 (
tan
0
0 60 1
E
E E
S
φ
and from 2a:
7. 
) cos(
1
0
S XV
XI
A
E
A
φ
+
=
Now that we know the A
XV
, A
XI
, and
φ
S
errors, we calculate the new calibration voltage gain coefficient from the
previous ones:
XV
NEW
A
V CAL
V CAL
_
_
=
We calculate PHADJ from
φ
S
, the desired phase lag:
[ ]
[ ] 





− − − −
− − − +
=
− −
− −
) 2 cos( ) 2 1 ( 1 ) tan( ) 2 sin( ) 2 1 (
) 2 cos( ) 2 1 ( 2 ) 2 1 ( 1 ) tan(
2
0
9
0
9
0
9 2 9
20
T f T f
T f
PHADJ
S
S
π φ π
π φ
And we calculate the new calibration current gain coefficient, including compensation for a slight gain increase
in the phase calibration circuit.
2 9
0
9
0
9 20 20
) 2 1 ( ) 2 cos( ) 2 1 ( 2 1
)) 2 cos( ) 2 1 ( 2 2 2 ( 2
1
1 _
_
− −
− − −
− + − −
− − +
+
=
T f
T f PHADJ PHADJ
A
I CAL
I CAL
XI
NEW
π
π
2.2.2 CALIBRATION WITH FIVE MEASUREMENTS
The five measurement method provides more orthogonality between the gain and phase error derivations. This
method involves measuring E
V
, E
0
, E
180
, E
60
, and E
300
. Again, set all calibration factors to nominal, i.e., CAL_IA
= 16384, CAL_VA = 16384, PHADJA = 0.
First, calculate A
XV
from E
V
:
1.  1
+ =
V XV
E A
Calculate A
XI
from E
0
and E
180
:
2. 1 ) cos( 1
) 0 cos(
) 0 cos(
0
− = −
−
=
S XI XV
S XI XV A A
IV
A A IV
E
φ
φ
3. 1 ) cos( 1
) 180 cos(
) 180 cos(
180
− = −
−
=
S XI XV
S XI XV A A
IV
A A IV
E
φ
φ
4.
2 ) cos( 2
180 0
− = +
S XI XV
A A E E
φ