JPH01218118A - Delay circuit - Google Patents

Abstract

PURPOSE:To delay a signal of a microwave band by millisecond or over by converting a microwave band signal into a low frequency, retarding the signal at a frequency region where the delay element whose delay is possible in millisecond or over and converting the frequency into the original frequency region. CONSTITUTION:A 1st frequency mixing circuit 2 receiving a signal at an input terminal 1, a 1st band pass filter using a frequency lower than the signal frequency of the input terminal 1 as its pass band, and a delay element 4 are provided to the circuit. Moreover, a 2nd frequency mixing circuit 5 receiving an output signal of the delay element 4 as the input, a 2nd band pass filter 6 using the frequency equal to the signal frequency of the input terminal 1 and passing through the output signal of the circuit 5 as the pass band and a local oscillation circuit 7 are provided to the circuit. Furthermore, the output signal of the local oscillation circuit 7 is branched to be fed to the 1st frequency mixing circuit 2 and the 2nd frequency mixing circuit 5 by a branch circuit 8 and also an output terminal 9 is provided. Thus, the microwave band signal is retarded by millisecond or over and the delay circuit without amplitude attenuation and waveform deterioration is obtained.

Description

[Detailed description of the invention] [Industrial application field] The present invention is suitable for use in microwave communication devices.

[Conventional technology]

SAW devices that utilize surface acoustic waves (SAW) are often used to delay signals in the microwave band. In order to increase the amount of delay in this SAW device, it is necessary to increase the size of the substrate used or to use a material with a low sound velocity. In addition to SAW devices, delay circuits using coaxial cables are also used.

[Means for solving problems]

However, in SAW devices, there is a limit to the absolute amount of delay, which is about 10 μsec at most. Since the amount of delay due to a unidirectional axial cable is constant at approximately 5 n5 ec/m, the absolute amount of delay is proportional to the length of the cable used. As the length of the cable increases, there are disadvantages such as amplitude attenuation and waveform deterioration. .

In this way, it is almost impossible to delay a microwave band signal by milliseconds or more using the circuit element described above.

SUMMARY OF THE INVENTION An object of the present invention is to provide a delay circuit for delaying a microwave band signal by milliseconds or more, and which does not cause amplitude attenuation or waveform deterioration.

[Means for solving problems]

The present invention converts a microwave band signal to a lower frequency, delays the signal in a frequency range in which a delay element capable of delaying milliseconds or more operates, and then converts the signal back to the original frequency range. This is the main feature, and differs from the conventional technology in that the signal is delayed in a low frequency region after frequency conversion.

[Effect]

The microwave is converted to a low frequency that allows the use of a delay element with a long time, and after a delay is given by the delay element, it is converted back to the original frequency. This makes it possible to use a wide variety of elements as delay elements, such as FIR digital filters, transfer devices such as CCDs or BBDs, or writing and reading to digital memories.

Further, since the first frequency mixing circuit and the second frequency mixing circuit use the same local oscillation frequency, even if there is a frequency fluctuation in the local oscillation frequency, this is canceled out and does not appear in the output.

Furthermore, by changing the local oscillation frequency, the phase of the delayed output signal can be changed.

〔Example〕

The figure is a block diagram of an apparatus according to an embodiment of the present invention.

This device includes a signal input terminal 1, a first frequency mixing circuit 2 which receives the signal of this input terminal 1, and a first bandpass filter whose pass band is a frequency lower than the signal frequency of the input terminal. 3 and a delay element 4 that operates at this low frequency.
, a second frequency mixing circuit 5 which receives the output signal of this delay element 4 as an input, and a second frequency mixing circuit 5 through which the output signal of this frequency mixing circuit 5 passes and whose pass band is equal to the signal frequency of the input terminal 1. a bandpass filter 6, a local oscillation circuit 7,
A branch circuit 8 that branches the output signal of the local oscillation circuit 7 and supplies it to the first frequency mixing circuit 2 and the second frequency mixing circuit 5 is connected to the output of the second bandpass filter 6. and an output terminal 9.

A microwave band signal with a frequency f and ±Δf input from the input terminal 1 is frequency-converted by the output signal of the local oscillation circuit 7 with an oscillation frequency f2, and when its unnecessary wave components are removed by the bandpass filter 3, the frequency becomes (f, -f2)±Δf. The local oscillation frequency f2 is selected such that the frequency is converted into the operating range of the delay element 4. Bandpass filter 30
The passband is (f+f2):Δf. Furthermore, the signal delayed by the delay element 4 is frequency-converted by the frequency mixing circuit 5, and unnecessary waves are filtered out by the bandpass filter 6.
When the signal is removed by , a delayed signal having the original frequency f1±Δf can be taken out from the output terminal 9.

In this embodiment, the delay element 4 is used as the delay element 4.
Impulse Re5ponse) digital filter was used.

The amount of delay (τ) becomes τ=N/f2 from the number of stages (N) of the digital filter and the sampling frequency (f,). For example, when N=200 and fs=50kHz, τ=4msec. Further, the upper limit usable frequency of the delay line in this example is 25 KHz. In order to increase the usable upper limit frequency, an FIR digital filter that operates in a region with an increased sampling frequency may be used. Also, FI
When an R digital filter is used in a delay line, arbitrary amplitude and delay characteristics can be provided by changing the coefficients.

Furthermore, a CCD (Charge Co., Ltd.) is used as a delay element.
(upledQevice), BBD (Buck
It is possible to use a transfer device such as a transfer device such as Etc. et Burigade Device), or a digital delay element that stores a digital signal obtained by once AD converting an input signal in a semiconductor memory, and after a certain period of time has elapsed, data read out from the memory is again DA converted and output.

After the microwave band signal is frequency-converted into the region where the delay element operates and delayed, it is frequency-converted back to the original frequency domain using the output from the same oscillator, so fluctuations in the local oscillation frequency during frequency conversion are caused by frequency down. It is canceled out during the up process and is not affected at all.

By changing the local oscillation frequency for frequency conversion, the phase of the output signal at the output terminal 9 can be changed. Since the phase rotation generated in the delay element 4 is determined by 2π(fl - f2)τ, the phase can be changed by changing the oscillation frequency f2 of the local oscillator.

〔Effect of the invention〕

As explained above, by using the present invention, signals in the microwave band can be delayed for milliseconds or more. Also,
By changing the local oscillation frequency, the phase of the delayed microwave band signal can be changed.

When a FIR digital filter is used in a delay line, it has the effect of being able to have arbitrary amplitude and delay characteristics by changing the coefficients.

[Brief explanation of the drawing]

The figure is a block diagram of an embodiment of the present invention. 1...Input terminal, 2...Frequency mixing circuit, 3...
Bandpass filter, 4... Delay element, 5... Frequency mixing circuit, 6... Bandpass filter, 7... Local oscillation circuit, 8...
...Distribution circuit, 9...Output terminal. Patent applicant: Nippon Telegraph and Telephone Corporation Representative Patent attorney: Naotaka Ide

Claims (1)

[Claims] 1. A delay circuit comprising a signal input terminal, a delay element, and a signal output terminal, comprising: a local oscillation circuit; and a signal at the input terminal and the output of the local oscillation circuit as inputs. a first frequency mixing circuit, through which the output signal of the frequency mixing circuit passes, the output signal being applied to the delay element, and a first bandpass filter having a passband having a frequency lower than the frequency of the signal at the input terminal. and a second frequency mixing circuit which receives the output signal of the delay element and the output of the local oscillation circuit, and the output signal of the frequency mixing circuit passes through and the output signal is connected to the output terminal and the input terminal. and a second bandpass filter with a passband equal to the signal frequency.