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4
Data Device Corporation
www.ddc-web.com
RD-19230
ERROR PROCESSOR
RINPUT
(
θ
)
VELOCITY
OUT
DIGITAL
POSITION
OUT (
φ
)
VCO
A
2
CT
1
S
H = 1
+
-
e
-2d/c
GAIN = 4
B
A
2A
-6dboc
10B
ω
(rad/sec)
2A
2 2 A
ω
(rad/sec)
f = BW (Hz) =
2 A
π
CLOSED LOOP
(B = A/2)
GAIN = 0.4
(CRITICALLY DAMPED)
OPEN LOOP
FIGURE 3.TRANSFER FUNCTION
BLOCK DIAGRAM #2
FIGURE 4. BODE PLOTS
TRANSFER FUNCTION AND BODE PLOT
The dynamic performance of the converter can be determined
from its Transfer Function Block Diagrams and Bode Plots (open
and closed loop).These are shown in FIGURES 2, 3, and 4.
The open loop transfer function is as follows:
where A is the gain coefficient and A
2
=A
1
A
2
and 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:
R
V
, R
B
, and C
BW
are selected by the user to set velocity scaling
and bandwidth.
- Error Gradient = 0.011 volts per LSB (CT + Error Amp + Demod
with 2 Vrms input)
- Integrator Gain = Cs Fs
1.1 C
BW
- VCO Gain = 1
1.25 R
V
C
VCO
where: Cs = 10 pF
Fs = 67 kHz when R CLK = 30 k
C
VCO
= 50 pF
A S
S S
+1
( )
10B
Open Loop Transfer Function =
GENERAL SETUP CONDITIONS
DDC has external component selection software which consid-
ers all the criteria below. In a simple fashion, it asks the key sys-
tem parameters (carrier frequency, resolution, bandwidth, and
tracking rate) needed to derive the external component values.
The following recommendations should be considered when
installing the RD-19230 R/D converter:
1) In setting the bandwidth (BW) and Tracking Rate (TR) (select-
ing five external components), the system requirements need to
be considered. For the greatest noise immunity, select the mini-
mum BW and TR the system will allow. Selecting a f
BW
that is
too low relative to the maximum application tracking rate can cre-
ate a spin-around condition in which the converter never settles.
The relationship to insure against this condition is detailed in
TABLE 2.
2) Power supplies are
±
5 VDC. For lowest noise performance it
is recommended that a 0.1
μ
F 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.
TABLE 2.TRACKING/BW RELATIONSHIP
RPS (MAX)/BW
1
0.50
0.25
0.125
RESOLUTION
10
12
14
16