JPS61156957A - Sine wave frequency detecting circuit - Google Patents

Abstract

PURPOSE:To attain the estimation of the frequency of the input sine wave by forming the circuit with a multiplier to which the output of a subtractor and that of the primary delay circuit are inputted and a signal processing part which consecutively renews its output and by making the output of the said processing part to be the secondary input to the said multiplier. CONSTITUTION:Delay circuits 10 and 11 that delay by a fixed time T are connected in series, whose respective outputs S1(t) and S3(t) are added by an adder 20 to obtain the output S4. Meanwhile, the output S2(t) from the delay circuit 10 and that 20 from a signal processing part 40 are multiplied by a multiplier 30, of which product that is S7(t) is subtracted by a subtractor 21 from the output S4(t) of the adder 20 to obtain an output S5(t). In the signal processing part 40, the output S5(t) of the subtractor 21 and that S2(t) of the delay circuit 10 are signal-processed so that the output S5(t) becomes smaller, for which the part 40 consecutively renews the output S6(t) of itself. From the value when this output signal S6(t) reaches the fixed value, the frequency of the input sine wave can be discriminated. In the result the input frequency can be discriminated regardless of the amplitude of the received input sine wave itself.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a sinusoidal frequency detection circuit for a single frequency input in a receiving section of a data transmission device using a single frequency signaling system.

[Prior art]

One type of data transmission apparatus is a system that uses a single frequency, and a typical example thereof is a facsimile transmission procedure. CCITT (International Telegraph and Telephone Consultative Committee)
Phases B and D as specified in Recommendation T.30
In the case of the G2 facsimile I7, a single frequency signal system is used as the signal used in the G2 facsimile I7.

Conventionally, such single-frequency input frequency detection circuits include those that detect each frequency by using a filter internally, and those that use delay detection. The latter method using delayed detection is shown in Figure 1. The circuit shown in FIG. 1 is comprised of a delay circuit 10 that delays by a fixed time T, a multiplier 30, and a low-pass filter 41. The input 5l(t) of the delay circuit 1o is a sine wave with a single frequency. That is,
5t (tl=A-sinωt (A: amplitude, ω: angular frequency) The output of the delay circuit is given by the following equation.

8(t-T)=A-sin[ω(tT)] Therefore,
The output of the multiplier 30 is. The first term in the above equation is a DC component, and the second term is an AC component with an angular frequency of 2ω. Therefore, by cutting the second term component with the low-pass filter 41,
Only the first term component can be output. That is,
The low-pass filter 41 depends only on the input amplitude and angular frequency ω.

Therefore, the frequency of a single frequency input can be detected from the magnitude of the output of the low-pass filter 41.

However, in the case of delay detection as shown in Fig. 1, as mentioned above, the magnitude of the output of the low-pass filter also depends on the input amplitude A, so The disadvantage is that a highly accurate AGO circuit is required. Also, if a filter is provided for each frequency, it will not be affected much by the amplitude level of the input, but as the number of types of frequencies for a single frequency input increases, it becomes necessary to prepare as many filters as there are types. However, the disadvantage is that the circuit size becomes large.

[Structure of the invention]

The sine wave detection circuit of the present invention is an adder that connects first and second delay circuits with equal delay times in cascade and calculates the sum of the input of the first delay circuit and the output of the second delay circuit. and,
a multiplier whose first input is the output of the first delay circuit; a subtracter that subtracts the output of the multiplier from the output of the adder; and the output of the subtracter and the first delay circuit. The output of the signal processing section is input to the multiplier, and the output of the signal processing section is used as the second input of the multiplier, and from the output value of the signal processing section, the sine of the input is It is characterized by being able to estimate the frequency of waves.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention, in which delay circuits 10 and 11 for delaying by a certain time 'r are connected in cascade, and the input 5t (tl) of the delay circuit IO and the output 5s of the delay circuit 11 are connected in series. (Add tl by adder 20 and output 8
4(tl is obtained. On the other hand, the output S2(t
) and the output 5s (tl) of the signal processing unit 40 are multiplied by the multiplier 30, and the output 5r (tl is subtracted from the output 5dt of the adder 20 using the subtracter 21) to obtain the output 5s (tl
get. In the signal processing unit 40, the output S5(
t) and the output 52(t) of the delay circuit 10, the output 8s(tl) is sequentially updated so that the signal 5S(t) becomes smaller.This output signal 85(
The frequency of the input sine wave can be determined from the value when t) reaches a steady value.

That is, when the input signal 5x (tl is a sinusoidal wave with a single frequency), the input signal S1 (tl can be expressed as 81(t) = A - sin (ωt). At this time, the output 5s of the adder 20 (tl is 8 <(tl = 8 tftl+ 83(t)=Syo(t)+5l(t2T) =A-sin(ωt)+A-sin(ω(t-2T)'
)=2A −sin (ω(t −′]′ ) ]
COs (G/r). On the other hand, the output 87(tl) of the multiplier 30 is 87(t)=S a(tl・8(t−T
)=5a(tl-A-5in(ω(t-T))
becomes. Therefore, when the signal 5s(tl reaches a steady value, the output S5(t) of the subtracter ideally becomes zero, that is, S4(t) = 87(t), the signal processing section 40 Output 8 a (tl is 8g(t) = 2・cos (ωT)), input 51 (the amplitude of tl is not transferred to the human body, and becomes a signal that depends only on the angular frequency ω. Therefore, the signal processing Part 4
The frequency of the input ax(tl) can be determined independently of its amplitude by the magnitude of the output signal 5s(tl) of zero.

As an example of the operation of the signal processing unit 40, a steepest slope algorithm is adopted. That is, Patent S5(tl/n+
,=85(tl8 to α·5s(tl·82ft+(α is a constant)) By updating 86(jl/n, the output 5s(tl) of the subtractor 21 can be made smaller.

〔Effect of the invention〕

As explained above, according to the present invention, the frequency of the input sine wave can be determined regardless of the amplitude of the received input sine wave, and even when there are many types of input sine waves, There is no need to increase the number of filters as in the past,
It can be provided with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional example, and FIG. 2 is a block diagram showing an embodiment of the present invention. 10.11...delay circuit, 20...adder, 21...subtractor, 3o...multiplier, 40...signal processing section , 41...Low pass filter. O Yu・1 top conflict 2 autopsy

Claims (1)

[Claims] a series circuit of first and second delay circuits having equal delay times;
an adder that calculates the sum of the sine wave input of the first delay circuit and the output of the second delay circuit; a multiplier whose first input is the output of the first delay circuit; and an output of the adder. a subtracter that subtracts the output of the multiplier from the subtracter; the output of the subtracter and the output of the first delay circuit are input, and the output is sequentially updated to be used as a second input of the multiplier; A sine wave frequency detection circuit comprising: a signal processing section that makes two inputs substantially equal, and detecting the frequency of the sine wave from an output value of the signal processing section.