Aeroflex NAV 2000R, Operation Manual, Page: 60 / 95

Aeroflex Operation Manual
NAV 2000R SIGNAL GENERATOR - REV. 0 – JULY 26, 2007 - PG 4-4
The Bus Request / Bus Grant circuitry is used by the microprocessor to control the DSP board and RF
Modulator Module busses. A Bus Request addresses a board or module. The board or module floats all
necessary local buss control lines and returns a Bus Grant. Each Bus Grant is an open collector output
simplifying their parallel connection.
The keyboard Bank Latch selects the bank of keyboard keys, upper or lower, which are read upon a key
press interrupt service read.
4.3.7 DSP BOARD THEORY OF OPERATION
The digital signal processor board of the NAV 2000R is designed around Analog Device's digital signal
processor, ADSP 2105. The board generates various fixed level complex waveforms. The digital signal
processor uses a sine lookup table ROM to obtain values for sine and cosine functions (reference DSP
Board Block diagram, JPN Drawing 40-5743-00, located in Section V of this manual). The DSP board
generates simple tones, frequency modulated tones and a combination of these signals. Digital data from
the DSP processor is sent to a 8 times oversampling digital filter whose output rate is 8 times higher than
the input sample rate. The digital filter adds additional reconstruction points according to the algorithm
and coefficients stored in the filter chip. The output of the digital filter is applied to a serial input 16 bit D/A
converter. The output of the D/A converter is passed through a 3 pole lowpass Butterworth filter. The
filtered output is available internally at the main connector. A buffered output is available through a BNC
connector.
The output function of the DSP board is divided into two modes: 1) VOR mode, 2) Alternate mode. In the
VOR mode, the output waveform is a combination of three tones with variable amplitude, with one of the
tones being frequency modulated. In alternate mode, the output waveform is a combination of a
maximum of three variable amplitude tones.
W t
ANGLE ACC
9960 Hz
c n
Z
−1
(32)
sin ( W t − COS W t )
c n
f
fm
% MOD 9960Hz
s c
W t
16BIT 16BIT
(32)
(32)
W t
v s
(32)
−1
Z
n m
30Hz REF
ANGLE ACC
W t
COS W t
m n
n v
sin W t
W t
ANGLE ACC
30Hz VAR
v s
Z
−1
(32)
s m
W t
(32)
(32)
W t
v s
(32)
−1
Z
n
I
IDENT f
ANGLE ACC
W t
sin W t
I n
1020Hz
OUTPUT V (Tn)
% MOD 30Hz
% MOD ID
16BIT 16BIT
16BIT 16BIT
fm
f
− ( )
NOTE:
PEAK DEVIATION ±480Hz
f
fm
−
=
480
30
= −16
−
m n
X
X
X
X