Novatech Instruments 408A - Operation

5
408A Manual
3.9
Signal Outputs.
There are three signal outputs
on the 408A: Sine (Q), Cosine (I) and ACMOS/
TTL. The Sine, Cosine and ACMOS/TTL are pro-
vided on BNC connectors on the front panel. Simply
connect your 50Ω application cable to appropriate
output. If you are not using the ACMOS/TTL out-
put, it is suggested that it be disabled by sending the
“A D” command for best system noise perfor-
mance.
NOTE:
Modes 1, 3 and 4 shown in the command table
require internal parallel connections. For maximum
shielding effectiveness, these connections are not
accessible on the 408A. See either the Model 2908A
or the Model DDS8m if you require these modes.
4.0
Operation
4.1 Power on reset. After power is applied, the
408A takes one second to initialize. Commands sent
during this time will be ignored or may cause erro-
neous operation.
4.2 Serial Operation. After the 408A has been
installed in the customer application system, all that
is required for operation is to send the appropriate
RS232 commands per Table 2.
4.3 The user host computer software must properly
format the serial commands. Incorrect formatting
will result in an error code being returned. See Table
1 for a list of RS232 error codes.
4.4 For maximum interface speed, it is suggested
that Echoing be disabled by the “E D” command.
This will allow the host to send characters at a faster
rate. Note that no flow control is provided. Depend-
ing upon your host, the 408A may not be able to pro-
cess all the serial characters. The 408A will respond
with an “OK” for a correctly received data com-
mand. You must verify correct operation at your host
rate.
4.5 If you are using an external clock, the value sent
to the 408A during the “F” command must be
scaled. The output frequency of the 408A when used
with an external clock is given by:
NOVATECH INSTRUMENTS
F
out
= (F
command
)*(F
ext clk
/F
int clk
)
NOTE:
An internal clock select jumper must be moved to
use an external clock. See the appendix for jumper
location.
4.6 The nominal Internal Clock has a nominal value
of 28.1474976710656 MHz. Best performance is
obtained when the External Clock input times the
Reference PLL multiplier (Kp) is close to the default
value (281.475MHz; max. 300MHz).
4.7 For an example, suppose an external clock of
10.000MHz is used and an output of 1.544MHz is
desired:
F
command
= (1.544)*(28.1474976710656)/10.0
= 4.345973640413
4.8 The command then sent to the 408A for the
1.544MHz output, with a 10MHz external clock,
will be (assuming Kp is unchanged):
f0 4.345973640413
NOTE:
You must account for your clock frequency error and
calculation roundoff when using an external clock
and the serial mode. Most hand calculators do not
have enough digits to match the resolution of the
408A.
4.9 Since the resolution of the 408A is 48-bits, the
typical fractional error for output frequencies in the
MHz range will be less than 1x10
-12
, even when
exact values are not possible. The Novatech Instru-
ments Model LPO30 can be used to lock to
external references and create signals without frac-
tional frequency error.
Typical ∆f/f for External Clock of 10.0MHz
Kp
Desired
Fout
Command
∆
f/f
10 1.544MHz
f0 4.345973640413
1.09x10
-13
20 1.544MHz
f0 2.172986820206
3.93x10
-13
10 2.048MHz
f0 5.764607523034
1.33x10
-13
20 2.048MHz
f0 2.882303761517
3.06x10
-13