rdc19220 ETC-unknow, rdc19220 Datasheet - Page 4

• Manufacturer Part Number: rdc19220
• Description: 16-bit Monolithic Tracking Resolver Lvdt -to-digital Converters
• Manufacturer: ETC-unknow

THEORY OF OPERATION
The RDC-19220 Series of converters are single CMOS custom
monolithic chips. They are implemented using the latest IC tech-
nology which merges precision analog circuitry with digital logic
to form a complete, high-performance tracking Resolver-to-
Digital converter. For user flexibility and convenience, the con-
verter bandwidth, dynamics and velocity scaling are externally
set with passive components.
FIGURE 1 is the functional block diagram of the RDC-19220
Series. The converter operates with ±5 Vdc power supplies.
Analog signals are referenced to analog ground, which is at
ground potential. The converter is made up of two main sections;
a converter and a digital interface. The converter front-end con-
sists of sine and cosine differential input amplifiers. These inputs
are protected to ±25 V with 2 k
the ±5 Vdc supplies. These amplifiers feed the high accuracy
Control Transformer (CT). Its other input is the 16-bit digital angle
Data Device Corporation
www.ddc-web.com
Notes for TABLE 1:(from previous page)
1. Unused data bits are set to logic “0.”
2. In LVDT mode, bit 16 is LSB for 14-bit resolution or bit 12 is LSB for
10-bit resolution.
3. Accuracy spec below for LVDT mode, null to + full scale travel (45
degrees).(2 wire-LVDT configuration).
degrees).(3 wire-LVDT configuration).
Note that this is the converter spec only and does not consider the
front end external resistor tolerances.
4. See text, General Setup Considerations and HigherTracking Rates.
5. See text: General Setup Considerations for RDC19222.
6. Any unused input pins may be left floating (unconnected). All input
pins are internally pulled-up to +5 Volts.
7. Ka = Acceleration constant, for a full definition see the RD/RDC
application manual acceleration lag section.
8. When using internally generated -5V, the internal -5V charge pump
when measured at the converter pin, can read as low as -20% (or -
4V).
9. No 180° hangup with A/C reference.
Accuracy spec below for LVDT mode, null to + full scale travel (90
4 Min part = 0.15% + 1 LSB of full scale “resolution set”.
2 Min part = 0.07% + 1 LSB of full scale “resolution set”
4 Min part = 0.07% + 1 LSB of full scale “resolution set”.
2 Min part = 0.035% + 1 LSB of full scale “resolution set”
RESOLVER
INPUT
(θ)
+
CT
-
FIGURE 2. TRANSFER FUNCTION BLOCK DIAGRAM #1
resistors and diode clamps to
GAIN
R S
DEMOD
11 mV/LSB
C F
-VSUM
S S
R 1
1
R B C
C
H = 1
BW
/10
BW
4
VEL
R
between the two inputs. The CT performs the ratiometric trigono-
metric computation of SIN COS - COS SIN = SIN( - ) using
amplifiers, switches, logic and capacitors in precision ratios.
Note: The transfer function of the CT is normally trigonometric,
The converter accuracy is limited by the precision of the com-
puting elements in the CT. For enhanced accuracy, the CT in
these converters uses capacitors in precision ratios, instead of
the more conventional precision resistor ratios. Capacitors, used
as computing elements with op-amps, need to be sampled to
eliminate voltage drifting. Therefore, the circuits are sampled at a
high rate (67 kHz) to eliminate this drifting and at the same time
to cancel out the op-amp offsets.
The error processing is performed using the industry standard
technique for type II tracking R/D converters. The dc error is inte-
grated yielding a velocity voltage which in turn drives a voltage
controlled oscillator (VCO). This VCO is an incremental integra-
tor (constant voltage input to position rate output) which togeth-
V
. Its output is an analog error angle, or difference angle,
-VCO
but in LDVT mode the transfer function is triangular (linear)
and could thereby convert any linear transducer output.
C
THRESHOLD
50 pf
Note: EM enables the MSBs and EL enables the LSBs.
VCO
1(MSB)
±1.25 V
VEL
BIT
TABLE 2. DIGITAL ANGLE OUTPUTS
10
11
12
13
14
15
16
2
3
4
5
6
7
8
9
VCO
UP/DOWN
COUNTER
16 BIT
DEG/BIT
0.7031
0.3516
0.1758
0.0879
0.0439
0.0220
0.0110
0.0055
11.25
5.625
2.813
1.405
22.5
180
90
45
OUTPUT
DIGITAL
(φ)
RDC-19220 SERIES
MIN/BIT
168.75
10800
337.5
84.38
42.19
21.09
10.55
5400
2700
1350
5.27
2.64
1.32
0.66
0.33
675
R-12/05-0