ADC1175-50EVAL National Semiconductor, ADC1175-50EVAL Datasheet - Page 16

• Manufacturer Part Number: ADC1175-50EVAL
• Description: BOARD EVALUATION FOR ADC1175-50
• Manufacturer: National Semiconductor

Specifications of ADC1175-50EVAL

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *ADC1175-50EVAL

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pling interval to vary, causing excessive output noise and a
reduction in SNR performance. Simple gates with RC timing
is generally inadequate as a clock source.
Input test signal contains harmonic distortion that inter-
feres with the measurement of dynamic signal to noise
ratio. Harmonic and other interfering signals can be removed
by inserting a filter at the signal input. Suitable filters are
shown in Figure 7 and Figure 8. The circuit of Figure 7 has
cutoff of about 5.5 MHz and is suitable for input frequencies
of 1 MHz to 5 MHz. The circuit of Figure 8 has a cutoff of about
11 MHz and is suitable for input frequencies of 5 MHz to 10
MHz. These filters should be driven by a generator of 75 Ohm
source impedance and terminated with a 75 ohm resistor.
FIGURE 8. 11 MHz Low Pass filter to eliminate harmonics
at the signal input. Use at input frequencies of 5 MHz to
FIGURE 7. 5.5 MHz Low Pass Filter to Eliminate
Harmonics at the Signal Input.
10 MHz
10009219
10009218
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Not considering the effect on a driven CMOS digital cir-
cuit(s) when the ADC1175 is in the power down mode.
Because the ADC1175 output goes into a high impedance
state when in the power down mode, any CMOS device con-
nected to these outputs will have their inputs floating when
the ADC is in power down. Should the inputs of the circuit
being driven by the ADC digital outputs float to a level near
2.5V, a CMOS device could exhibit relative large supply cur-
rents as the input stage toggles rapidly. The solution is to use
pull-down resistors at the ADC outputs. The value of these
resistors is not critical, as long as they do not cause excessive
currents in the outputs of the ADC1175. Low pull-down resis-
tor values could result in degraded SNR and SINAD perfor-
mance of the ADC1175. Values between 5 kΩ and 100 kΩ
should work well.