LTC1065_09 Datasheet, PDF (6/16 Pages) Linear Technology – DC Accurate, Clock-Tunable Linear Phase 5th Order Bessel Lowpass Filter

LTC1065
TYPICAL PERFOR A CE CHARACTERISTICS
Transient Response
HORIZONTAL: 0.1ms/DIV, VERTICAL: 2V/DIV
V_S = ±5V, f_C = 10kHz, V_IN = 1kHz ±3V_P
SQUARE WAVE
1065 G16
Group Delay
45
40
35
30
25
20
15
10
5
V_S = ±5V
f_C = 10kHz
0
0 3 6 9 12 15
INPUT FREQUENCY (kHz)
18 21
1065 G17
PI FU CTIO S
Power Supply Pins (Pins 6, 3, N Package)
The positive and negative supply pin should be bypassed
with a high quality 0.1µF ceramic capacitor. In applications
where the clock pin (5) is externally swept to provide
several cutoff frequencies, the output DC offset variation
is minimized by connecting an additional 1µF solid tanta-
lum capacitor in parallel with the 0.1µF disc ceramic. This
technique was used to generate the graphs of the output
DC offset variation versus clock; they are illustrated in the
Typical Performance Characteristics section.
When the power supply voltage exceeds ±7V, and when
V ^– is applied before V⁺ (if V⁺ is allowed to go below
ground) connect a signal diode between the positive
supply pin and ground to prevent latch-up (see Typical
Applications).
Ground Pin (Pin 2, N Package)
The ground pin merges the internal analog and digital
ground paths. The potential of the ground pin is the
reference for the internal switched-capacitor resistors,
and the reference for the external clock. The positive input
of the internal op amp is also tied to the ground pin.
For dual supply operation, the ground pin should be
connected to a high quality AC and DC ground. A ground
plane, if possible, should be used. A poor ground will
6
degrade DC offset and it will increase clock feedthrough,
noise and distortion.
A small amount of AC current flows out of the ground pin
whether or not the internal oscillator is used. The fre-
quency of the ground current equals the frequency of the
clock. The average value of this current is approximately
55µA, 110µA, 170µA for ±2.5V, ±5V and ±7.5V supplies
respectively.
For single supply operation, the ground pin should be
preferably biased at half supply (see Typical Applications).
V_OS Adjust Pin (Pin 8, N Package)
The V_OS adjust pin can be used to trim any small amount
of output DC offset voltage or to introduce a desired output
DC level. The DC gain from the V_OS adjust pin to the filter
output pin equals two.
Any DC voltage applied to this pin will reflect at the output
pin of the filter multiplied by two.
If the V_OS adjust pin is not used, it should be shorted to the
ground pin. The DC bias current flowing into the V_OS adjust
pin is typically 10pA.
The V_OS adjust pin should always be connected to an AC
ground; AC signals applied to this pin will degrade the filter
response.
1065fb