Programmable filter

1、 Programmable Filter Description

Krohn Hite 3945 modelHigh pass/low-pass Butterworth/Bessel programmable filtersProvide a tunable low-pass Butterworth channel within the range of 170Hz to 25.6MHz; The Butterworth or Bessel channel with two independent low-pass, high pass, or bypass channels and one channel bandpass or bandstop can be adjusted within the range of 3Hz to 2MHz.

The 3945 model is designed specifically for applications that require high-frequency bandpass filtering. The peak cut-off frequency of the filter can be set to any frequency between 170Hz and 10MHz, and the cut-off frequency of the low-end filter can be set to any frequency between 3Hz and 2MHz.

2、 50MHz Low Noise Amplifier

One channel of the 3945 model can operate as a low-noise amplifier, bypassing the filter, providing a bandwidth of 50MHz, and achieving a bandwidth of up to 46dB. This is useful for users who wish to increase signal gain and improve signal-to-noise ratio before filtering. The other two channels of the 3945 model provide Bessel or Butterworth transfer functions, which can be programmed as two low-pass, high pass, and one bandpass or bandstop filters with a gain of 40dB per channel.

3、 Non-volatile memory

The 3945 filter provides 99 sets of non-volatile memory for storing front panel settings, stored in battery powered CMOS. Settings can be called using simple commands. Perform self check diagnosis when powered on to ensure that all internal memory is working properly. If a malfunction occurs, the display screen will indicate which ROM or RAM is faulty.

4、 Application of Programmable Filters

The 3945 model can provide filtering for many applications, such as high-frequency anti aliasing for digital signal processing, EMI testing, video recording, and more. The 3945 model is carefully designed for users, providing ease of operation, reliability, and price competitiveness.

5High pass/low-pass Butterworth/Bessel programmable filtersInstruction Manual

Specification suitable for 25 ℃± 10 ℃

6、 Function

Channels 1.1 and 1.2: Low pass, high pass, or bypass of two independent channels; Bandpass or bandstop of a channel

Channel 2.1: A low-pass filter channel or amplification bypass

7、 Filter characteristics of channels 1.1 and 1.2

Type: 4-pole Butterworth (planar maximum) or Bessel (linear phase)

Attenuation slope: 24dB/octave per channel

Adjustable frequency range (fc): 3Hz to 2MHz

Frequency resolution: 1Hz from 3Hz to 1kHz; 10Hz at 2kHz; 100Hz at 100kHz; 1kHz at 1MHz; 10kHz at 2MHz

Cut off frequency accuracy (fc): ± 2%, minimum significant figure (larger) 20Hz to 500kHz; ± 5%, reaching 2MHz

Relative gain fc: Butterworth, -3dB; Bessel, -7.58dB

Bandwidth: When DC coupling, from DC to FC; when AC coupling (low-pass), from 0.2Hz to FC; when AC coupling (high pass), from FC to 10MHz.

Passband response (0dB, input/output gain): ± 0.5dB at 2MHz

Bandstop attenuation:>80dB

Harmonic distortion: -80dB at 1kHz and 1Vrms.

Noise (reference input): Using a 2MHz bandwidth detector for<200 μ V

Input:

Pre filter gain: 0dB or 20dB; ± 0.2dB

Coupling: AC or DC

Impedance: 1M Ω parallel 100pf

Peak signal (gain at 0dB): Peak voltage at fc<1MHz is ± 4.5V; peak voltage at 2MHz is ± 4V

Peak DC blocking voltage: ± 200V in AC coupling mode

output:

Post filter gain: 0dB or 20dB; ± 0.2dB.

Impedance: 50 Ω

Voltage peak: The peak voltage is ± 6.5V at ³ 500 Ω and ± 1.3V at ³ 50 Ω

Peak current: ± 25mA

DC level: adjustable zero

DC stability: typical value is ± 0.5mV/℃; Peak value is ± 1mV/℃

8、 Channel 2.1 Filter Characteristics

Filter type: 4-pole, Butterworth, low-pass.

Attenuation slope: 24dB/octave band

Adjustable cut-off frequency range: 170Hz to 25.6MHz

Frequency resolution: 10Hz from 170Hz to 2.56kHz; 100Hz from 2.6kHz to 25.6kHz; 1kHz from 26kHz to 256kHz; 10kHz from 260kHz to 2.56MHz; From 2.6MHz to 25.6MHz, it is 100kHz.

Cut off frequency accuracy: ± 2% at 2.56MHz and ± 5% at 25.6MHz.

Passband response: ± 0.2dB at 2.56MHz and ± 0.5dB at 25.6MHz.

Bandstop attenuation: -100dB at 1MHz; -75dB at 10MHz; -55dB at 30MHz; -50dB at 50MHz; -40dB at 100MHz.

Input/output coupling: AC or DC, with an AC coupling cut-off frequency of approximately 16Hz at the input and 10Hz at the output. Note that the internal 50 Ω input is connected before the AC coupling.

Noise spectral density (10kHz to 100MHz reference input): Below -128dBm/Hz at 50 Ω, this translates to broadband noise power or voltage of 30MHz BW below -53dBm or 500 μ Vrms for the input.

Harmonic distortion (1Vrms sine wave): greater than -60dB at 100kHz (0.1%) of the signal, all harmonics below 50dB at 1MHz, and below 40dB above 1MHz.

Stray signal: below -80dBm at 65MHz; Below -75dBm at 100MHz. The inputs expressed in voltage form are 22mV and 40mV, respectively.

DC stability: reference input is ± 0.5mV/℃

Input:

Pre filter gain: 0dB,+10dB,+20dB; ±0.1dB

Impedance: optional 1M Ω or 50 Ω, ± 2%, shunt 65pF

Signal peak: The peak voltage at 0dB gain is ± 1.5V, which decreases proportionally to the gain setting.

Lossless input peak: 12Vrms when the input terminator is turned off, 7Vrms when the input terminator is turned on

Peak DC blocking voltage: 200V. Note that the internal input terminal is connected before AC coupling and can only withstand 7Vrms when turned on.

output:

Post filter gain: 0dB,+6dB,+20dB,+26dB; ± 0.1dB.

Impedance: 50 Ω, ± 2%.

Signal peak value: ± 3V when open circuit; ± 1.5V when 50 Ω

DC level: adjustable zero

9、 Amplifier mode characteristics (only 2.1 channels)

Bandwidth:>50MHz

Input:

Pre filter gain: 0dB,+10dB,+20dB; ±0.1dB

Impedance: optional 1M Ω or 50 Ω, ± 2%, shunt 65pF

Signal peak: The peak voltage at 0dB gain is ± 1.5V, which decreases proportionally to the gain setting.

Lossless input peak: 12Vrms when the input terminator is turned off, 7Vrms when the input terminator is turned on.

Peak DC blocking voltage: 200V. Note that the internal input terminal is connected before AC coupling and can only withstand 7Vrms when turned on.

Post filter gain: 0dB,+6dB,+20dB,+26dB; ± 0.1dB.

Impedance: 50 Ω, ± 2%

Signal peak value: ± 3V when open circuit; ± 1.5V when 50 Ω

DC level: adjustable zero

Rise and fall time:<7ns at 0dB input gain and 6dB output gain,; At+20dB input or output gain, it is<10ns; at ringing or overshoot, it is<5%.

10、 Conventional

Frequency control: keyboard input or up/down arrow keys

Memory: 99 optional groups; The memory is a non-volatile battery powered CMOS.

Overload mode (channel 2.1 only): Three optional modes: non locked, monitoring all channels and prioritizing the display of channels with overload; Lock, maintain overload display, clear overload; No instructions.

Overload indicator (only applicable to channel 2.1): LED for input and output. When the display channel is overloaded, the gain display flashes.

Self check diagnosis: The MPU checks the unit when powered on, and the display screen indicates the fault mode.

Display: 7 segments, green, LED； 0.3 inches high

Remote programming: IEEE-488.1 interface. Including: SH1, AH1, T6, L4, SR1, RL1, PP1, DC1, DT0, C0, E1.

Working temperature: 0 ℃ to 50 ℃

Chassis isolation: ± 200Vdc

Storage temperature: -20 ℃ to 70 ℃

Input/output interface: BNC, panel and rear side

Power requirements: 90-132/180-264 volts AC, 50Hz-400Hz, 35 watts.

Dimensions: 3.5 inches (9cm) high, 14 inches (36cm) wide, 12.5 inches (32.13cm) deep

Weight: 12 pounds (5.4kg) net weight, 14 pounds (6.3kg) gross weight

Attachment: 6-pin, three terminal power cord; Operation Manual

11、 Optional

020: The low-frequency cut-off frequency range is 0.3Hz to 200kHz

Rack installation kit: part number RK-37, allows installation of model 3945 into a standard rack spacing of 19 feet.

Extended 1-year warranty: Part number EW3945

12、 Optional attachments

CAB-010: GPIB cable with connector, 2 meters

CAB-011: GPIB cable with connector, 1 meter

CAB-025: Cable, BNC，3ft， low noise

13、 High frequency bandpass operation

Connecting the output of channel 1.1 or 1.2 (set as high pass) to the input of channel 2.1 (set as low-pass, 50 Ω input impedance, 6dB output gain) provides a bandpass filter with 0dB insertion loss. The low-end cutoff frequency is adjustable between 3Hz and 2MHz, and the peak cutoff frequency is adjustable between 170Hz and 10MHz. When the peak cutoff frequency is set above 10MHz, the passband response will deteriorate.

The manual is subject to change without prior notice