AD650 Analog Devices, Inc., AD650 Datasheet - Page 9

• Manufacturer Part Number: AD650
• Description: Voltage-to-frequency And Frequency-to-voltage Converter
• Manufacturer: Analog Devices, Inc.

If the approximate amount of noise that appears on C
(V
inequality:
For example, consider an application calling for a maximum
frequency of 75 kHz, a 0 V to 1 V signal range, and supply
voltages of only ±9 V. The component selection guide of Figure 9
is used to select 2.0 kΩ for R
in a one-shot time period of approximately 7 μs. Substituting
75 kHz into Equation 7 yields a value of 1300 pF for C
the input signal is near zero, 1 mA flows through the integration
capacitor to the switched current sink during the reset phase,
causing the voltage across C
Because the integrator output stage requires approximately 3 V
headroom for proper operation, only 0.5 V margin remains for
integrating extraneous noise on the signal line. A negative noise
pulse at this time could saturate the integrator, causing an error
in signal integration. Increasing C
provides much more noise margin, thereby eliminating this
potential trouble spot.
NOISE
C
), then the value of C
INT
>
+
t
V
OS
S
−
×
3
1
V
×
10
−
V
−
3
NOISE
INT
INT
A
IN
can be checked using the following
to increase by approximately 5.5 V.
and 1000 pF for C
INT
to 1500 pF or 2000 pF
OS
. This results
INT
INT
is known
. When
Rev. D | Page 9 of 20
(8)
100kHz
10kHz
1MHz
1000
100
20
INPUT
RESISTOR
Figure 10. Typical Nonlinearity vs. C
Figure 9. Full-Scale Frequency vs. C
16.9k
40.2k
100k
50
20k
50
100
ONE SHOT CAPACITOR
100
C
OS
C
(pF)
OS
(pF)
1000
1000
OS
OS
INPUT
RESISTOR
16.9k
20k
40.2k
100k
AD650