WO2008050928A1

WO2008050928A1 - Intermediate frequency converter for electronic measuring instrument

Info

Publication number: WO2008050928A1
Application number: PCT/KR2006/004873
Authority: WO
Inventors: Jae-Hyoung Cho; Chul-Soo Lim; Hyun Jee; Hyun-Min Roh
Original assignee: Gs Instruments Co., Ltd.
Priority date: 2006-10-27
Filing date: 2006-11-20
Publication date: 2008-05-02
Also published as: KR100824017B1

Abstract

Disclosed relates to an intermediate frequency converter for an electronic measuring instrument, such as a frequency spectrum analyzer having a broad range of frequencies, which converts an input frequency signal into an intermediate frequency required in the electronic measuring instrument. In a measuring instrument processing input frequency signals having a broadband frequency range, the intermediate frequency converter for an electronic measuring instrument in accordance with the present invention comprises: a first intermediate frequency circuit for converting an input frequency signal into a primary intermediate frequency signal in accordance with its frequency band; a second intermediate frequency circuit for converting the primary intermediate frequency signal into an intermediate frequency signal for the process of the measuring instrument; and a control unit for controlling the first and second intermediate frequency circuits, the primary intermediate frequency signal being set to at least first and second frequency values based on the band of the input signal, and the first and second frequency values being set within a frequency band range to be input to the measuring instrument.

Description

[DESCRIPTION]

[invention Title]

INTERMEDIATE FREQUENCY CONVERTER FOR ELECTRONIC MEASURING

INSTRUMENT

[Technical Field]

The present invention relates to an electronic measuring instrument such as a frequency spectrum analyzer and, more particularly, to an intermediate converter for an electronic measuring instrument that converts a frequency of an input signal into an intermediate frequency required in the electronic measuring instrument.

[Background Art] In general, various kinds of measuring instruments have been used for carrying out experiments or developing new products in electric and electronic fields. Such measuring instrument includes an oscilloscope, a spectrum analyzer and the like. The measuring instrument is used for analyzing input analog signals such as frequency signals (RF signal) .

In the general communication equipments or measuring instruments, if the frequency of the input signals are not regular but variable, the frequencies of the corresponding input signal are converted into an intermediate frequency to process the signal efficiently. Such conversion into the intermediate frequency is achieved by mixing an appropriate local oscillation frequency in accordance with the frequency of the input signal. Like this, in the process of mixing frequencies, frequency signals corresponding to the sum and difference of the input signal frequency and the local oscillation frequency are generated. In general, a frequency signal is selected from these signals to use as an intermediate frequency signal and the other frequency signals are removed through a filter.

Meanwhile, in selecting an intermediate frequency, a frequency other than the input frequencies is selected to avoid the problems of crosstalk and noise with the input frequencies. However, since the frequency of the signals input to the measuring instrument such as spectrum analyzer has a broad range of 1001(Hz to 3 GHz, it is necessary to select a frequency over 3 GHz as the intermediate frequency. If the frequency of the signal processed in such instrument is increased over 3 GHz, the unit prices of elements applied to the instrument are increased and, in case of a substrate, it is necessary to use a Teflon substrate of high price, not a general FR4 substrate. That is, it has a drawback in that the price of the instrument becomes very high. Moreover, it still has a drawback in that the design of the instrument for processing signals of high frequency becomes very complicated.

[Disclosure] [Technical Problem] The present invention has been contrived taking the above-described circumstances into consideration and, an object of the present invention is to provide an intermediate frequency converter that can be applied to an electronic measuring instrument that processes a broad range of input frequencies for the measurement.

[Technical Solution]

To accomplish the object of the present invention, there is provided an electronic measuring instrument processing input frequency signals having a broadband frequency range, wherein an intermediate frequency converter for an electronic measuring instrument comprising: a first intermediate frequency circuit for converting an input frequency signal into a primary intermediate frequency signal in accordance with its frequency value; a second intermediate frequency circuit for converting the primary intermediate frequency signal into a final intermediate frequency signal for the process of the measuring instrument; and a control unit for controlling the first and second intermediate frequency circuits, the primary intermediate frequency signal being set to at least first and second frequency values based on the frequency of the input signal, and the first and second frequency values being set within a frequency band range to be input to the measuring instrument .

Moreover, the intermediate frequency converter for an electronic measuring instrument further comprises an input pad, through which a user sets a frequency of a signal to be input to the measuring instrument. Furthermore, the first intermediate frequency circuit comprises: a plurality of first filters for filtering the input frequency signal according to the band; a first mixer for mixing a local oscillation frequency signal with a frequency signal output from the first filter; and a local oscillation circuit for generating the local oscillation frequency signal.

In addition, the local oscillation circuit comprises: a PLL circuit for generating a voltage corresponding to a control data from the control unit; a voltage controlled oscillator for generating a frequency signal corresponding to the voltage output from the PLL circuit; a frequency multiplier for multiplying the frequency signal output from the voltage controlled oscillator; and a first switching unit for selectively inputting the frequency signals, output from the voltage controlled oscillator and the frequency multiplier, to the first mixer as a local oscillation frequency signal, the voltage controlled oscillator including first to fourth varactor diodes coupled to an input voltage in parallel. Additionally, the second intermediate frequency circuit comprises: a plurality of second filters for filtering the first or second frequency signal from the frequency signal input from the first intermediate frequency circuit; a plurality of second mixers for mixing a local oscillation frequency signal with a frequency signal output from the first filter, respectively; and a second switching unit for selectively outputting the frequency signal output from the second mixer as an intermediate frequency signal, the local oscillation frequency signals, applied to the second mixers, having a frequency value different from each other.

[Description of Drawings]

The above and other features of the present invention will be described with reference to certain exemplary embodiments thereof illustrated the attached drawings in which:

Fig. 1 is a block diagram depicting an intermediate frequency converter for an electronic measuring instrument in accordance with a preferred embodiment of the present invention;

Fig. 2 is a block diagram showing a concrete configuration of a first IF circuit 2 of Fig. 1;

Fig. 3 is a circuit diagram illustrating a concrete configuration of a voltage controlled oscillator 282 of Fig. 2 ; and

Fig. 4 is a block diagram showing a concrete configuration of a second IF circuit 3 of Fig. 1.

[Mode for the invention]

Hereinafter, the preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. In the below embodiment, the description will be made by exemplifying a spectrum analyzer to which the present invention is applied. However, such exemplification is not intended to limit the scope of the present invention. The present invention can be applied and embodied to the general measuring instruments such as oscilloscope besides the frequency spectrum analyzer in the same manner.

Fig. 1 is a block diagram depicting an intermediate frequency converter for an electronic measuring instrument in accordance with a preferred embodiment of the present invention. In the figure, a frequency signal that is input to the measuring instrument for the measurement is amplified through an amplifier 1 and input to a first IF circuit 2. The first IF circuit 2 converts the input frequency signal based on a control data DATA and switching signals SWl to SW4 applied from a control unit 5, to be described hereinafter, into a primary intermediate frequency (IF) signal .

The signal input from the outside through the amplifier 1 has a frequency in the range of 100 kHz to 3 GHz. The first IF circuit 2 converts the input frequency signal into a first or a second IF signal based on the frequency value of the input signal. Here, 749.275MHz is used as the first IF signal and 287.525MHz is used as the second IF signal, for example. The first or second IF signal output from the first IF circuit 2 is input to a second IF circuit 3. The second IF circuit 3 frequency-converts the primary IF signal input from the first IF circuit 2 into a final IF signal, i.e., an actual IF signal based on switching signals SW5 to SW7 applied from the control unit 5. The frequency of the IF signal output from the second IF circuit 3 is set at 58.075MHz, for example.

An input pad 4 is provided so that a user operates the measuring instrument. The input pad 4 includes selection buttons, through which the user selects the frequency range for the measurement, the same as the general one.

The control unit 5 controls the overall measuring instrument. Especially, if the frequency range is set by the input pad 4, the control unit 5 controls the first and second IF circuits 2 and 3 appropriately based on the set values. The control operation of the control unit 5 will be described in detail below.

Fig. 2 is a block diagram showing a concrete configuration of the first IF circuit 2 of Fig. 1. In the figure, the frequency signal input from the outside through the amplifier 1 is input to a switching unit 21. Then, the switching unit 21 selectively inputs the input frequency signal to a low pass filter (LPF) 22, a band pass filter (BPF) 23 or a high pass filter (HPF) 24 based on the switching signal SWl from the control unit 5. Here, the low pass filter 22 is set to have a frequency pass band under 1.2GHz, the band pass filter 23 is set to have a frequency pass band of 1.2 GHz to 2.0GHz, and the high pass filter 24 is set to have a frequency pass band more than 2.0GHz, for example. Such filters 22 to 24 are to remove other input signals than the frequency band selected by the user. Here, the output from the low pass filter 22, the band pass filter 23 or the high pass filter 24 is linked to an input of a switching unit 25. The switching unit 25 selectively outputs the input frequency signal based on the switching signal SW2 from the control unit 5. The frequency signal output like this is applied to a mixer 27 through an amplifier 26 and mixed with a local oscillation signal applied from a local oscillation circuit 28. Referring back to Fig. 1, the control unit 5 controls the switching units 21 and 25 based on the measuring frequency set through the input pad 4 and inputs the input frequency signals to the mixer 27 through the filters 22 to 24 corresponding to the frequency. The local oscillation circuit 28 generates a local oscillation frequency in a range of 600 MHz to 2.8GHz based on the control data DATA and the switching signals SWl to SW4 and applies the local oscillation frequency to the mixer 27. The control unit 5 applies the control data DATA and the switching signals SW3 and SW4 to the local oscillation circuit 28 based on the measuring frequency set through the input pad 4. Moreover, the control unit 5 controls the local oscillation circuit 28 to set a local oscillation frequency within a range of 600 MHz to 1.4GHz, if the measuring frequency set through the input pad 4 is less than 2.1 GHz, and set a local oscillation frequency within a range of 1.2 GHz to 2.8 GHz, if is exceeds 2.1GHz, for example, respectively. Of course, the local oscillation frequency generated from the local oscillation circuit 28 will be set at appropriate values so that the first IF signal is of 749.275MHz and the second IF signal is of 287.525MSz, for example.

The following Table 1 depicts the local oscillation frequencies generated from the local oscillation circuit 28 corresponding to the frequencies of the input signals.

[Table 1]

The local oscillation frequency is set according as the control unit 5 inputs an appropriate control data DATA to the local oscillation circuit 28. Meanwhile, a PLL circuit 281 in the local oscillation circuit 28 outputs a voltage in a range of 0 to 28V, for example, based on the control data DATA applied from the control unit 5 and an oscillated frequency fed back from an output end of a voltage controlled oscillator (VCO) 282. The voltage controlled oscillator 282 generates and outputs a frequency signal of 600 MHz to 1.4GHz for the input voltage of 0 to 28V. The output of the voltage controlled oscillator 282 is input to a switching unit 284 and, then, the switching unit 284 selectively inputs the input signal to a frequency multiplier 285 or a switching unit 286 based on the switching signal SW3 applied from the control unit 5. The frequency multiplier 285 multiplies the frequency signal of 600 MHz to 1.4GHz input through the switching unit 284 double to generate a frequency signal of 1.2 GHz to 2.8GHz, and the frequency signal generated like this is input to the switching unit 286. The switching unit 286 selectively inputs the frequency signal, applied from the switching unit 284 or the frequency multiplier 285, to the mixer 27 as a local oscillation frequency based on the switching signal SW4 from the control unit 5. Meanwhile, since the local oscillation circuit 28 generates a local oscillation frequency signal in the range of 600 MHz to 2.8 GHz in the above configuration, it is required to configure the voltage controlled oscillator 282 having a broad band range of 600 MHz to 1.4GHz. Fig. 3 is a circuit diagram illustrating an example of the configuration of the voltage controlled oscillator 282, which is configured by modifying the conventional Colpitts circuit partially.

In the figure, input ends to which a voltage of a predetermined level is input from the PPL circuit 281 are coupled to cathodes of varactor diodes Dl and D2 in parallel through a resistance Rl and with cathodes of varactor diodes D3 and D4 in parallel through a resistance R2.

Moreover, anode of the varactor diode Dl is grounded through a resistance R4 and, at the same time, connected to an input end of an amplifying circuit 283 through a capacitor Cl, and anode of the varactor diode D2 is grounded through an inductor Ll and a resistance R3. Anode of the varactor diode D3 is grounded, and anode of the varactor diode D4 is grounded through a resistance R3. Here, the inductor Ll is composed of a micro strip line for the minimization of power consumption, and the varactor diodes Dl to D4 having a capacitance variable range of 5pF to 4OpF, for example, are used for the applied voltage in the range of 0 to 28V.

The oscillation frequency (f_o) of the oscillation circuit has the following Equation 1, supposed that the total inductance value is L_t, and the total capacitance value is Ct: [Equation 1]

Here, since the input ends of the oscillation circuit are coupled to the varactor diodes Dl and D2 in parallel, those are linked to the varactor diode D3 and D4 in parallel, and the capacitor Cl is connected to the varactor diode Dl in series, the total capacitance value C_t of the oscillation circuit may be expressed by the following Equation 2 : [Equation 2] C_t = (D₁//'D₂) //C₁+ (D₃//D₄) wherein Dx to D₄ mean capacitance values that the varactor diodes Dl to D4 have, and Ci denotes a capacitance value that the capacitor Cl has .

Accordingly, if the inductance value of the inductor Ll is 2.3nH, for example, the oscillation frequency of the oscillation circuit has a range of 600 MHz to 1.4GHz for the input voltage of 0 to 28V. Meanwhile, Fig. 4 is a block diagram showing a concrete configuration of the second IF circuit 3 of Fig. 1. In the figure, the primary IF signal, i.e., the first or second IF signal, input from the first IF circuit 2 is selectively input to band pass filters 32 and 33 through a switching unit 31. The switching unit 31 is switching- controlled in accordance with the switching signal SW5 applied from the control unit 5. The control unit 5 controls the switching unit 31 based on the frequency set through the input pad 4 to connect the first IF signal, i.e., the primary IF signal including a frequency of 749.275MHz, to an input of the band pass filter 32, and the second IF signal, i.e., the primary IF signal including a frequency of 287.525MHz to an input of the band pass filter 33.

The band pass filter 32 has a frequency characteristic in that the center frequency is 749.275MHz and the band width is 10 MHz, and the band pass filter 33 has a frequency characteristic in that the center frequency is 287.525 MHz and the band width is 10 MHz.

As depicted in Table 1, the control unit 5 controls the local oscillation circuit 28 in accordance with the frequency set through the input pad 4, i.e., the frequency of the input signal, and generates a predetermined local oscillation frequency signal. The local oscillation frequency signal generated like this is applied to the mixer 27 of Fig. 2 and mixed with the input frequency signal. Here, the mixer 27 generates and outputs a sum frequency signal and a difference frequency signal of the local oscillation frequency signal and the input frequency signal, and these frequency signals are input to the second IF circuit 3.

That is, if the frequency of the input signal is 549.99MHz, this signal is mixed with a local oscillation frequency signal of 1,299.265 MHz, as can be seen from Table 1, in the mixer 27. Accordingly, the difference frequency signal of 749.275MHz and the sum frequency signal of

1,849.255MHz are generated from the mixer 27 and input to the second IF circuit 3. If the frequency range selected through the input pad 4 is within 0.1~549.99 MHz, the control unit 5 controls the switching unit 31 to connect the input signal from the first IF circuit 2 to an input of the band pass filter 32. Accordingly, in this case, a first IF signal having a frequency of 749.275MHz is output from the band pass filter 32.

The following Table 2 depicts the frequencies of the primary IF signal selected in accordance with the frequencies of the input signals.

[Table 2]

As described in detail above, the primary IF signal is generated from the first IF circuit 2 by subtracting or adding the input frequency signal from or to the local oscillation frequency. Moreover, the control unit 5 controls the switching unit 31 of Fig. 4 based on the data depicted in Table 2 to selectively input the primary IF signal from the first IF circuit 2 to the band pass filters 32 and 33.

Subsequently, the first or second IF signal output from the band pass filters 32 and 33 is applied to the mixer 34 or 35 and mixed with the local oscillation frequency signal, as will be described henceforth. In Fig. 4, the PLL circuit 36 generates a frequency signal of 345.6MHz for example, and this signal is coupled selectively to a frequency multiplier 38 and a band pass filter 40 through a switching unit 37. The switching unit 37 is also switching-controlled based on the switching signal SW7 applied from the control unit 5. As described above, the control unit 5 controls the switching unit 37 based on the frequency range selected through the input pad 4.

The frequency multiplier 38 multiplies the frequency signal of 345.6MHz applied from the PLL circuit 35 through the switching unit 37 double to generate a frequency signal of 691.2MHz. This frequency signal generated like this is applied to the mixer 34 as a local oscillation frequency signal through a band pass filter 39.

Furthermore, the band pass filter 40 applies the frequency signal of 345.6MHz, applied from the PLL circuit 36 to the switching unit 37, to the mixer 35 as a local oscillation frequency signal.

The mixer 34 mixes a first IF signal of 749.275MHz applied through the band pass filter 32 with the local oscillation frequency signal of 691.2MHz applied through the band pass filter 39 and outputs a frequency signal including a frequency signal of 58.075MHz. Meanwhile, the mixer 35 mixes a second IF signal of 287.525MHz applied through the band pass filter 33 with the local oscillation frequency signal of 345.6MHz applied through the band pass filter 40 and outputs a frequency signal including a frequency signal of 58.075MHz.

Like this, the frequency signals output through the mixers 34 and 35 are selectively output through a switching unit 41. The switching unit 41 is switching-controlled according to the switching signal SW6 applied from the control unit 5 in the same manner as the switching unit 31 described above .

Although not depicted in the figure, the frequency signal output through the switching unit 31 is filtered through the band pass filter and, thereby, a frequency signal of 58.075MHz is input as the final IF signal to the measuring instrument.

In the above configuration, the frequency signal input from the outside is converted into a primary IF signal by the first IF circuit 2. As depicted in Table 1, the first IF circuit 2 generates first and second IF signals having a different frequency from each other in accordance with the frequency band of the input signal. Especially, as can be learned from Table 1, the primary IF signal generated from the first IF circuit 2 is set to be within the range of the input signal frequencies and, at the same time, have a band frequency different from the corresponding input signal frequency. The first or second IF signal, output from the first IF circuit 2, is frequency-converted in the second IF circuit 3 and, consequently, the final IF signal having the same frequency signal is generated.

Accordingly, in the above described embodiment, it is possible to convert an input frequency signal having a frequency range of about 100 kHz to 3 GHz, for example, into an IF signal of a relatively low frequency, removing crosstalk or interference.

As above, the preferred embodiment of the present invention has been described. However, the above-described embodiment is one of the desirable examples of the present invention and the present invention can be embodied with various modifications within the range, not departing from the spirit and scope of the present invention. For example, in the above embodiment, the description has been made as for the input frequency signal converted into the first or second IF signal in the first IF circuit 2, however, it is possible to use at least two primary IF signals. Moreover, it is possible to select and use any other frequency values that do not overlap the frequency band of the input signal and the frequency band of the primary IF signal, not restricting the frequency values of the local oscillation signals and the IF signals used in the above embodiment . Furthermore, the description has been made as for the control unit 5 that executes the IF conversion by controlling the first and second IF circuits 2 and 3 in accordance with the frequency range set through the input pad 4, however, it is possible to carry out the IF conversion through a method in that a means for distinguishing the frequency of input signals is established and the control unit 5 controls the first and second IF circuit 2 and 3 in accordance with the distinguished results

[industrial Applicability]

According to the present invention as described above, it is possible to materialize an intermediate frequency converter that can be applied to an electronic measuring instrument in which the range of the input frequencies for the measurement is very broad.

Claims

[CLAIMS]

[Claim l]

An electronic measuring instrument processing input frequency signals having a broadband frequency range, wherein an intermediate frequency converter for an electronic measuring instrument comprising: a first intermediate frequency circuit for converting an input frequency signal into a primary intermediate frequency signal in accordance with its frequency value; a second intermediate frequency circuit for converting the primary intermediate frequency signal into a final intermediate frequency signal for the process of the measuring instrument; and a control unit for controlling the first and second intermediate frequency circuits, the primary intermediate frequency signal being set to at least first and second frequency values based on the frequency of the input signal, and the first and second frequency values being set within a frequency band range to be input to the measuring instrument.

[Claim 2]

The intermediate frequency converter for an electronic measuring instrument as recited in claim 1 further comprising an input pad, through which a user sets a frequency of a signal to be input to the measuring instrument .

[Claim 3] The intermediate frequency converter for an electronic measuring instrument as recited in claim 1, wherein the first intermediate frequency circuit comprises : a plurality of first filters for filtering the input frequency signal according to the band; a first mixer for mixing a local oscillation frequency signal with a frequency signal output from the first filter; and a local oscillation circuit for generating the local oscillation frequency signal.

[Claim 4]

The intermediate frequency converter for an electronic measuring instrument as recited in claim 3, wherein the local oscillation circuit comprises: a PLL circuit for generating a voltage corresponding to a control data from the control unit; a voltage controlled oscillator for generating a frequency signal corresponding to the voltage output from the PLL circuit; a frequency multiplier for multiplying the frequency signal output from the voltage controlled oscillator; and a first switching unit for selectively inputting the frequency signals, output from the voltage controlled oscillator and the frequency multiplier, to the first mixer as a local oscillation frequency signal, the voltage controlled oscillator including first to fourth varactor diodes coupled to an input voltage in parallel .

[Claim 5]

The intermediate frequency converter for an electronic measuring instrument as recited in claim 1, wherein the second intermediate frequency circuit comprises : a plurality of second filters for filtering the first or second frequency signal from the frequency signal input from the first intermediate frequency circuit; a plurality of second mixers for mixing a local oscillation frequency signal with a frequency signal output from the first filter, respectively; and a second switching unit for selectively outputting the frequency signal output from the second mixer as an intermediate frequency signal, the local oscillation frequency signals, applied to the second mixers, having a frequency value different from each other.