RU221361U1 - Digital filter with phase-frequency response pre-correction - Google Patents

Abstract

The utility model relates to radio engineering and other areas of electronic technology that use digital processing of a narrow-band signal, and can be used to filter a modulated signal and to correct phase shifts of a carrier wave. The purpose of the utility model is to implement a digital filter with a typical zero and atypical equivalent phase response. A digital filter with pre-correction of the phase-frequency characteristic contains a signal generation block with double the frequency of the carrier oscillation of the input signal, the input of which is connected to the input of the device, and the output is connected to the first input of the mixer, a narrow-band filter, the input of which is connected to the output of the mixer, and the output is the output of the device, the block delay, the input of which is connected to the input of the device, and the output is connected to the second input of the mixer.

Description

The utility model relates to radio engineering and other areas of electronic technology that use digital processing of a narrow-band signal, and can be used to filter a modulated signal and to correct phase shifts of a carrier wave.

As an analogue, we can consider a block for converting the initial phase of a harmonic signal in a frequency deviation converter of a periodic signal, containing a first mixer, both inputs of which and the input of a multistage bandpass amplifier are connected to the input of the initial phase converter block, a second mixer, the first input of which is connected to the output of the mixer, The output of the multistage bandpass amplifier is connected to the second input, and the output is the output of the initial phase converter [1].

The disadvantages of the known device are spectrum distortion when using a modulated signal due to the multiplication of the signal by itself in the first mixer.

A known device [2] (prototype) is a “digital filter with zero phase-frequency response” (PFC), containing a first narrow-band filter, the input of which is the input of the device, and the output is connected to the first input of the mixer, a signal generation unit with double the carrier frequency of the input signal, the input of which is connected to the input of the device, and the output is connected to the second input of the mixer, the second narrow-band filter, the input of which is connected to the output of the mixer, and the output is the output of the device.

The disadvantage of the known device is the difficulty of obtaining a given phase response, which requires changing the order of the first narrow-band filter, and this requires changing the values of all coefficients, of which there are thousands. Changing the order of the filter leads to a change in the slope of its phase response, which makes it possible to change the equivalent phase response of a known device.

The purpose of the useful model is to implement, using simple means, a digital filter with pre-correction of the phase response, which makes it possible to obtain a typical equivalent phase response (the increment of the phase shift as a function of frequency in the filter passband has a negative sign), a zero equivalent phase response (the increment of the phase shift as a function of frequency is zero) and an atypical equivalent Phase response (the increment in the phase shift as a function of frequency in the filter passband has a positive sign), as well as a decrease in frequency response distortion.

The technical result that can be obtained by using the utility model is the elimination of additional phase shifts in the carrier frequency that occur during conventional filtering of a modulated signal and the elimination of ambiguity in the values of phase shifts in the filter frequency band.

In fig. Figure 1 shows a block diagram of a digital filter with phase response pre-correction.

The device contains a delay unit 1, a unit 2 for separating the second harmonic component of the carrier of the input signal, a mixer 3 and a narrow-band filter 4.

The input of Delay Block 1 is connected to the input of the device, and the output is connected to the first input of mixer 3, the input of signal generation block 2 with double the carrier frequency of the input signal is connected to the input of the device, and the output is connected to the second input of mixer 3, the input of narrowband filter 4 is connected to the output mixer 3, and the output is the output of the device.

A digital filter with phase response pre-correction works as follows.

The non-distorting delay block 1 has a linear typical phase response. When a narrowband signal passes through delay block 1, the initial phases of its harmonic components will receive corresponding increments, and the carrier oscillation will receive an additional phase increment: . Using block 2, a carrier oscillation is isolated from the signal spectrum, the frequency of which is then doubled. In this case, the initial phase is also doubled. In mixer 3, the signal coming from the output of delay unit 1 and the signal with double the frequency of the carrier signal are multiplied. The output of mixer 3 will be a signal containing two spectra. The first spectrum is determined by the difference frequencies of the harmonics of the multiplied signals, and the second by the total frequencies. The second spectrum is suppressed by narrowband filter 4 and is not taken into account further. The initial phase of the carrier oscillation of the first spectrum, as a result of subtracting the frequencies and initial phases in the mixer, will take the form: . The sign of the phase shift obtained in delay block 1 changes. If the phase shift of the carrier wave in narrowband filter 4 is equal to the phase shift in delay block 1, then the equivalent phase shift of the carrier wave at the output of the device will be zero, and the equivalent phase response will be zero. By changing the delay time of delay block 1, you can obtain a mode of undercompensation of the phase shift of filter 4 or overcompensation. Accordingly, we obtain modes with a typical or atypical equivalent phase response of the device.

Changing the delay time in digital devices is not a complicated procedure and is implemented in real time.

The equivalent phase response of a device can be converted from a range of several tens of radians to a range of units or fractions of radians, which eliminates ambiguity.

The implementation of an atypical phase response and its use in frequency deviation converters of periodic signals makes it possible to create converters with controlled sensitivity.

The equivalent frequency response of the device coincides with the frequency response of a narrow-band filter.

The results of modeling and implementation of a digital filter according to the structure shown in Fig. 1 confirm the conclusions drawn.

List of sources for consideration during the examination:

1. Patent 2214034 MPK ⁷ H 03 B 21/04 Device for converting frequency deviation of a periodic signal. Shakursky V.K., Ivanov V.V. Publ. 10.10.2003. Bull. No. 28.

2. Shakursky, M.V. Digital filter with zero phase-frequency characteristic / V.K. Shakursky, M.V. Shakursky // Pat. on useful model 109619 Russian Federation, MPK H03H 9/00; publ. 10/20/2011 Bulletin. No. 29.

Claims (1)

A digital filter with pre-correction of the phase-frequency characteristic, containing a signal generation unit with double the frequency of the carrier oscillation of the input signal, the input of which is connected to the input of the device, and the output is connected to the first input of the mixer, a narrow-band filter, the input of which is connected to the output of the mixer, and the output is the output of the device, characterized in that a delay block is introduced into it, the input of which is connected to the input of the device, and the output is connected to the second input of the mixer.