National Instruments NI 5401 用户手册

Chapter 2

Function Generator Operation

©

 National Instruments Corporation

2-9

The SYNC output is a TTL version of the sine waveform generated at the 
output. The signal from the pre-amplifier is sent to a comparator, where it 
is compared against a level set by the level DAC. The output of this 
comparator is sent to the SYNC connector through a hysteresis buffer and 
a 50 

Ω

 series resistor to reverse terminate reflected pulses.

You can use the SYNC output as a very high-frequency resolution, 
software-programmable clock source for many applications. You also can 
vary the duty cycle of SYNC output, on the fly, by changing the output of 
the level DAC. The SYNC output might not carry meaning for other types 
of generated waveforms.

You can change the duty cycle of the SYNC output at any time during waveform 

generation. 

Figure 2-10 shows the NI 5401 output attenuator chain. The output 
attenuators are made of resistor networks and may be switched in any 
combination. The maximum attenuation possible on the NI 5401 is 73 dB.

Figure 2-10.  Output Attenuation Chain

By attenuating the output signal, you keep the dynamic range of the DAC; 
that is, you do not lose any bits from the digital representation of the signal 
because the attenuation is done after the DAC and not before it.

attenuation (in decibels) = –20 log

10

 (V

o

 /V

i

)

where V

o

 = desired voltage level for the output signal

V

i

 = input voltage level.

For the NI 5401, V

i

 = ±5 V for a terminated load and ±10 V for an 

unterminated load.

1 dB

16 dB

2 dB

4 dB

8 dB

32 dB

Out

In