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LT1568

Very Low Noise, High Frequency Active RC, Filter Building Block

Linear Technology 

LT1568

FILTER ELECTRICAL CHARACTERISTICS

Specifications are for the differential output (OUTA – OUTA or OUTB – OUTB) of a single 2nd order section (A or B), gain = –2,

RFIL = R11 = R21 = R31 = R12 = R22 = R32. All voltages are with respect to VGND = VGNDA = VGNDB. The q denotes the specifications

which apply over the full operating temperature range, otherwise specifications and typical values are at TA = 25°C.

VS = single 5V, EN pin to logic “low,” RLDIFF = 800Ω connected to midsupply, unless otherwise noted.

SYMBOL PARAMETER

CONDITIONS

MIN TYP MAX UNITS

Filter Gain Mismatch

(VOUTA – VOUTA) – (VOUTB – VOUTB)

Wideband Output Noise

fC = 1MHz, fIN = fC

fC = 10MHz, fIN = fC

fC = 1MHz, RFIL = 1.28k, BW = 2MHz

fC = 10MHz, RFIL = 128Ω, BW = 20MHz

q –0.3 ±0.10 0.3

dB

q –0.4 ±0.15 0.4

dB

36

µVRMS

88

µVRMS

THD

Total Harmonic Distortion

fC = 1MHz, RFIL = 1.28k,

fIN = 200kHz, VIN = 1VP-P

– 84

dB

fC = 10MHz, RFIL = 128Ω,

fIN = 2MHz, VIN = 1VP-P

– 69

dB

Note 1: Absolute Maximum Ratings are those values beyond which the life

of the device may be impaired.

Note 2: The inputs of each op amp are protected by back-to-back diodes.

If either differential input voltage exceeds 1.4V, the input current should be

limited to less than 10mA.

Note 3: A heat sink may be required to keep the junction temperature

below the absolute maximum rating when the output is shorted

indefinitely.

Note 4: The inverter bandwidth is measured with the SA or SB output

floating, and is defined as the frequency at which the phase shift from

OUTA (OUTB) to OUTA (OUTB) drops from 180° to 135°.

Note 5: Measured with the SA or SB output connected in the filter

application circuit as shown in the Block Diagram.

Note 6: The common mode input voltage range is measured by shorting

the filter input to the common mode reference (GNDA or GNDB) and

applying a DC input voltage to search for the common mode voltage range

that creates a ±2mV (VS = 3V) or ±5mV (VS = ±5V) change in the (OUTA

or OUTB) voltage (measured with respect to GNDA or GNDB).

Note 7: The minimum cutoff frequency of the LT1568 is arbitrarily listed

as 200kHz. The limit is arrived at by setting the maximum resistor value

limit at 6.4k. Due to input bias current, the output DC offset through a

single section can be as high as 25mV with resistors this large. The

LT1568 can be used with even larger resistors if the large offset voltages

can be tolerated. For cutoff frequencies below 200kHz, refer to the

LTC1563-2, LTC1563-3.

Note 8: With equal-sized resistors, the differential DC gain through either a

single section or cascaded sections is 6dB.

Note 9: The LT1568C is guaranteed to meet specified performance from

0°C to 70°C. The LT1568C is designed, characterized and expected to

meet specified performance from –40°C to 85°C but is not tested or QA

sampled at these temperatures. The LT1568I is guaranteed to meet

specified performance from –40°C to 85°C.

1568f

6

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