RDC-19220/2S
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®
16-BIT MONOLITHIC TRACKING
RESOLVER-TO-DIGITAL CONVERTER
FEATURES
•
Accuracy up to 2.3 Arc Minutes
•
Internal Synthesized Reference
•
+5 Volt Only Option
•
Programmable:
- Resolution: 10-, 12-, 14-, or 16-Bit
- Bandwidth
- Tracking Rate
•
Differential Resolver Input Mode
•
Velocity Output Eliminates
Tachometer
•
Built-In-Test (BIT) Output,
No 180° Hangup
DESCRIPTION
The RDC-19220/2S is a low-cost versatile state-of-the-art 16-bit
monolithic Resolver-to-Digital Converter. This single chip converter
offers programmable features such as resolution, bandwidth and
velocity output scaling.
Resolution programming allows selection of 10, 12, 14, or 16 bits,
with accuracies to 2.3 minutes. This feature combines the high track-
ing rate of a 10-bit converter with the precision and low-speed veloc-
ity resolution of a 16-bit converter in one package.
The internal Synthesized Reference section eliminates errors due to
quadrature voltage. Previously, a 6 degree phase shift caused prob-
lems for a 16-bit converter. The synthesized reference capability
ensures operation with a phase shift up to 45 degrees.
The velocity output (VEL) from the RDC-19220/2S, which can be
used to replace a tachometer, is a 4 V signal referenced to ground.
The full-scale value of VEL is set by the user with a single resistor.
The RDC-19220/2S converter is available with operating temperature
ranges of 0° to +70°C, -40° to +85°C, and -55° to +125°C.
•
-55° to +125°C Operating
Temperature
APPLICATIONS
The low cost, small size, high accuracy, and versatile performance of
the RDC-19220/2S converter makes it ideal for use in modern high
performance industrial control systems. Typical applications include
motor control, radar antenna positioning, machine tool control, robot-
ics, and process control.
FOR MORE INFORMATION CONTACT:
Data Device Corporation
105 Wilbur Place
Bohemia, New York 11716
631-567-5600 Fax: 631-567-7358
www.ddc-web.com
Technical Support:
1-800-DDC-5757 ext. 7382
©
1999, 2000 Data Device Corporation
Data Device Corporation
www.ddc-web.com
RDC-19220
SERIES
SYNTHESIZED
REFERENCE
(RDC1922XS ONLY)
SIGNAL
INPUTS
SIN
-S
+S
COS
-C
+C
+5C
+CAP
-CAP
-5C
A GND
+5 V
GND
-5 V
-
+
A B
-
+
CONTROL
TRANSFORMER
GAIN
REFERENCE
INPUT
+REF -REF
BIT
EXTERNAL
COMPONENTS
(RC MAY BE LEFT
UNCONNECTED)
VSUM
C
BW
R
1
DEMODULATOR
C
BW
10
R
B
VEL
2
RDC-19220/2S
E-11/02-300
HYSTERESIS
16-BIT
UP/DOWN
COUNTER
E
DATA
LATCH
VCO
&
TIMING
INTEGRATOR
R
V
-5 V
INVERTER
(RDC-19222
ONLY)
VCO
R
S
R
C
POWER SUPPLY
INPUTS/GROUND
INH
EM BIT 1 EL
THRU
BIT 16
A B
RESOLUTION
CONTROL
CB
DIGITAL
OUTPUT
FIGURE 1. RDC-19220/2S BLOCK DIAGRAM
TABLE 1. RDC-19220/2S SPECIFICATIONS
These specifications apply over the rated power supply, tempera-
ture, and reference frequency ranges; 15% signal amplitude varia-
tion & 10% harmonic distortion.
PARAMETER
UNIT
VALUE
RESOLUTION
Bits
10, 12, 14, or 16 (notes 1 & 2)
FREQUENCY RANGE
Hz 47-1k(note 4) 1k - 4k
4k - 10k
ACCURACY -XX2
Min 4 +1 LSB 4 +1 LSB 5 +1 LSB
-XX3
(NOTE 3) Min 2 +1 LSB 2 +1 LSB 3 +1 LSB
REPEATABILITY
LSB ± 1
±1
± 2
DIFFERENTIAL LINEARITY
LSB ± 1
±1
± 2
REFERENCE
(+REF, -REF)
Type
Differential
V ±10 max
Voltage: differential
V ±5 max
single ended
V ±25 continuous 100 transient
overload
Hz DC to 10,000
Frequency
Ohm 10M min //20 pf
Input Impedance
SIGNAL INPUT
(+S, -S, SIN, +C, -C, COS)
Type
Resolver, differential, groundbased
Vrms 2 ±15%
Voltage: operating
V
overload
±25 continuous
Ohm 10M min //10 pf.
Input Impedance
REFERENCE
(note 5)
±Sig/Ref Phase Shift
deg 45 max from 400 Hz to 10 kHz
DIGITAL INPUT/OUTPUT
Logic Type
TTL/CMOS compatible
Inputs
Logic 0 = 0.8 V max.
Logic 1 = 2.0 V min.
Loading=10 µA max P.U. current
source to +5 V //5 pF max.
CMOS transient protected
Inhibit (INH)
Logic 0 inhibits; Data stable
within 0.1 µS
Enable Bits 1 to 8 (EM)
Logic 0 enables; Data stable
Enable Bits 9 to 16 (EL)
within 150 nS
Logic 1 = High Impedance
Data High Z within 100 nS
Resolution and Mode
Control (A & B)
Mode
B
A Resolution
(see notes 1 and 2)
Resolver 0
0
10 bits
“
0
1
12 bits
“
1
0
14 bits
“
1
1
16 bits
LVDT -5 V
0
8 bits
“
0 -5 V
10 bits
“
1 -5 V
12 bits
“
-5 V -5 V
14 bits
Outputs
Parallel Data (1-16)
10, 12, 14 or 16 parallel lines;
natural binary angle positive
logic (see note 2)
Converter Busy (CB)
0.25 to 0.75 µs positive pulse
leading edge initiates counter
update.
Built-in-Test (BIT)
Logic 0 for BIT condition.
±100 LSBs of error with a filter of
500 µS total, Loss-of-Signal (LOS)
less than 500 mV, or Loss-of-
Reference (LOR) less than 500 mV.
TABLE 1. RDC-19220/2S SPECIFICATIONS (CONT.)
PARAMETER
DIGITAL INPUT/OUTPUT
Outputs (continued)
Drive Capability
UNIT
VALUE
DYNAMIC
CHARACTERISTICS
Resolution
Tracking Rate-min(note 6)
Bandwidth(Closed Loop) Max
Ka
A1
A2
A
B
Acceleration (1 LSB lag)
Settling Time(179° step)
VELOCITY
CHARACTERISTICS
Polarity
Voltage Range(Full Scale)
Scale Factor Error
Scale Factor TC
Reversal Error
Linearity
Zero Offset
Zero Offset TC
Load
Noise
POWER SUPPLIES
Nominal Voltage
Voltage Range
Max Volt. w/o Damage
Current
TEMPERATURE RANGE
Operating
-30X
-20X
-10X
50 pF+
Logic 0; 1 TTL load, 1.6 mA at
0.4 V max.
Logic 1; 10 TTL loads, -0.4 mA
at 2.8 V min
Logic 0; 100 mV max driving CMOS
Logic 1; +5 V supply minus 100 mV
min driving CMOS High Z; 10 uA //5
pF max
(at maximum bandwidth)
bits
rps
Hz
1/sec
2
1/sec
1/sec
1/sec
1/sec
deg/s
2
msec
10
1152
1200
5.7M
19.5
295k
2400
1200
2M
2
12
288
1200
5.7M
19.5
295k
2400
1200
500k
8
14
72
600
1.4M
4.9
295k
1200
600
30k
20
16
18
300
360k
1.2
295k
600
300
2k
50
V
%
PPM/C
%
%
mV
µV/C
kΩ
Vp/V
V
%
V
mA
Positive for increasing angle
±4 (at nominal ps)
10 typ
20 max
100 typ
200 max
0.75 typ 1.3 max
0.25 typ 0.50 max
5 typ
10 max
15 typ
30 max
8 max
1 typ
0.125 min, 2 max
(note 6 and 7)
+5
-5
±5
±5
+7
-7
14 typ, 22 max (each)
°C
°C
°C
0 to +70
-40 to +85
-55 to +125
Notes: 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 in LVDT mode is 0.15% + 1 LSB of full scale.
4. If the frequency is between 47Hz and 1kHz, then there may
be 1 LSB of jitter at quadrant boundaries.
5. The maximum phase shift tolerance will degrade linearly
from 45 degrees at 400 Hz to 30 degrees at 60 Hz.
Storage
°C -65 to +150
-30X or -20X
°C -65 to +150
-10X
THERMAL RESISTANCE
Junction to Case,
θjc
°C/W 92.4
40 Pin DDIP (Plastic)
°C/W 4.6
40 Pin DDIP (Ceramic)
°C/W 72.6
44 Pin J-Lead (Plastic)
°C/W 2.4
44 Pin J-Lead (Ceramic)
PHYSICAL
CHARACTERISTICS
in(mm) 2.0 x 0.6 x 0.2 (50.8 x 15.24 x 5.08)
Size: 40-pin DDIP
in(mm) 0.690 square (17.526)
44-pin J-lead
Weight:
40-pin DDIP
44-pin J-lead
Plastic
0.21 (5.95)
0.08 (2.27)
Ceramic
0.24 (6.80)
0.064 (1.84)
oz (g)
oz (g)
Notes: 6. See text, General Setup Considerations.
(cont.) 7. When using internally generated -5V the internal -5V charge pump
when measured at the converter pin, may be as low as -20% (or -4V).
Data Device Corporation
www.ddc-web.com
3
RDC-19220/2S
E-11/02-300
THEORY OF OPERATION
The RDC-19220/2S series of converter is a single CMOS custom
monolithic chip. It is implemented using mixed signal CMOS
technology 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 RDC-19220/2S Functional Block Diagram. The
converter operates with ±5 V DC 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 consists of sine and
cosine differential input amplifiers. These inputs are protected to
±25 V with 2 kΩ resistors and diode clamps to the ±5 V DC sup-
plies. These amplifiers feed the high accuracy Control
Transformer (CT). Its other input is the 16-bit digital angle
φ.
Its
output is an analog error angle, or difference angle, between the
two inputs. The CT performs the ratiometric trigonometric com-
putation of SINθCOSφ - COSθSINφ = SIN(θ-φ) using amplifiers,
switches, logic and capacitors in precision ratios.
Note:
The transfer function of the CT is normally trigonometric,
but in LVDT mode the transfer function is triangular (linear)
and could thereby convert any linear transducer output.
The converter accuracy is limited by the precision of the com-
puting elements in the CT. In this converter ratioed capacitors are
used in the CT, instead of the more conventional precision
ratioed resistors. 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 (70 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
integrated yielding a velocity voltage which in turn drives a volt-
age-controlled oscillator (VCO). This VCO is an incremental inte-
grator (constant voltage input to position rate output) which,
together with the velocity integrator, forms a type II servo feed-
RB C
BW
back loop. A lead in the frequency response is introduced to sta-
bilize the loop and a lag at higher frequency is introduced to
reduce the gain and ripple at the carrier frequency and above.
The settings of the various error processor gains and break fre-
quencies are done with external resistors and capacitors so that
the converter loop dynamics can be easily controlled by the user.
TRANSFER FUNCTION AND BODE PLOT
The dynamic performance of the converter can be determined
from its Transfer Function Block Diagrams and its Bode Plots
(open and closed loop). These are shown in FIGURES 2, 3, and 4.
The open loop transfer function is as follows:
Open Loop Transfer Function =
(
S + 1
)
B
S
S
(
10B + 1
)
A
2
2
where:
A is the gain coefficient
A
2
= A
1
A
2
B is the frequency of lead compensation
The components of gain coefficient are error gradient, integrator
gain, and VCO gain. These can be broken down as follows:
- Error Gradient = 0.011 volts per LSB (CT+Error
Amp+Demod with 2 Vrms input)
- Integrator gain =
- VCO Gain =
C
S
F
S
1.1C
BW
volts per second per volt
1
LSBs per second per volt
1.25 R
v
C
vco
C
s
= 10 pF
F
s
= 70 kHz when Rs = 30 kΩ
F
s
= 100 kHz when Rs = 20 kΩ
F
s
= 125 kHz when Rs = 15 kΩ
C
vco
= 50 pF
where:
R
V
, R
B
, and C
BW
are selected by the user to set velocity scaling
and bandwidth.
VEL
C
BW
/10
RS
-VSUM
R
V
VEL
-VCO
50 pf
C
VCO
CT
RESOLVER
INPUT
(θ)
+
GAIN
DEMOD
R1
VCO
1
C
S
F
S
11 mV/LSB
±1.25 V
THRESHOLD
-
16 BIT
UP/DOWN
COUNTER
H=1
DIGITAL
OUTPUT
(φ)
FIGURE 2. TRANSFER FUNCTION BLOCK DIAGRAM #1
Data Device Corporation
www.ddc-web.com
4
RDC-19220/2S
E-11/02-300
GENERAL SETUP CONDITIONS
DDC has external component selection software which consid-
ers all the criteria below and, in a simple fashion, asks the key
parameters (carrier frequency, resolution, bandwidth, and track-
ing rate) to derive the external component values.
The following recommendations should be considered when
installing the RDC-19220/2S R/D converter:
1) When setting the bandwidth (BW) and Tracking Rate (TR)
(selecting five external components), the system requirements
need to be considered. For the greatest noise immunity, select
the minimum BW and TR the system will allow.
2) Power supplies are ±5V DC. For lowest noise performance it
is recommended that a 0.1µF or larger cap be connected from
each supply to ground near the converter package.
3) Resolver inputs and velocity output are referenced to AGND.
This pin should be connected to GND near the converter pack-
age. Digital currents flowing through ground will not disturb the
analog signals.
4) The BIT output, which is active low, is activated by an error of
approximately 100 LSBs. During normal operation, for step
inputs or on power up, a large error can exist.
5) Setup of bandwidth and velocity scaling for the optimized crit-
ically damped case should proceed as follows:
- Select the desired f
BW
(closed loop), based on overall
system dynamics.
- Select fcarrier
≥
3.5 f
BW
- Compute R
v
= 55 kΩ x
{
For the converter max tracking rate value,
see the row indicated in TABLE 3.
}
Application max rate
8
- Compute C
BW
(pF) =
3.2 x F
S
(Hz) x 10
R
V
x (f
BW
)
2
- Where FS = 70 kHz for R
S
= 30 kΩ
100 kHz for R
S
= 20 kΩ
125 kHz for R
S
= 15 kΩ
- Compute R
B
=
- Compute C
BW
10
6) Selecting a f
BW
that is too low relative to the maximum appli-
cation tracking rate can create a spin-around condition in which
the converter never settles. The relationship to insure against
spin-around is as follows (TABLE 2.):
0.9
C
BW
x f
BW
TABLE 2. TRACKING/BW RELATIONSHIP
RPS (MAX)/BW
1
0.50
0.25
0.125
RESOLUTION
10
12
14
16
GAIN = 4
2A
OPEN LOOP
VELOCITY
OUT
VCO
A
2
S
DIGITAL
POSITION
OUT (φ)
-1
2d
b/o
(CRITICALLY DAMPED)
(B = A/2)
ct
B
A
-6
db
ω
(rad/sec)
10B
/oc
t
ERROR PROCESSOR
RESOLVER
INPUT
(θ)
+
-
CT
e
A1 S + 1
B
S
S +1
10B
GAIN = 0.4
f
BW
= BW (Hz) =
2A
2 2A
2A
π
H=1
CLOSED LOOP
ω
(rad/sec)
FIGURE 3. TRANSFER FUNCTION
BLOCK DIAGRAM #2
Data Device Corporation
www.ddc-web.com
5
FIGURE 4. BODE PLOTS
RDC-19220/2S
E-11/02-300
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