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LTC1063CS

DC Accurate, Clock-Tunable 5th Order Butterworth Lowpass Filter

Linear Technology 

LTC1063

TYPICAL PERFOR A CE CHARACTERISTICS

Transient Response

HORIZONTAL: 0.1ms/DIV, VERTICAL: 2V/DIV

VS = ±5V, fC = 10kHz, VIN = 1kHz ±3VP

SQUARE WAVE

1063 G16

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

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

internal or external 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).

VOS Adjust Pin (Pin 8, N Package)

The VOS 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 VOS 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 VOS adjust pin is not used, it should be shorted to the

ground pin. The DC bias current flowing into the VOS adjust

pin is typically 10pA.

Pin 8 should always be connected to an AC ground; AC

signals applied to this pin will degrade the filter response.

Input Pin (Pin 1, N Package)

Pin 1 is the filter input and it is connected to an internal

switched-capacitor resistor. If the input pin is left floating,

the filter output will saturate. The DC input impedance of

pin 1 is very high; with ±5V supplies and 1MHz clock, the

DC input impedance is typically 1GΩ. A resistor, RIN, in

series, with the input pin will not alter the value of the

6

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