Abstract:
A decimal frequency synthesizer in which, for each decade, two identical sets of four arithmetic progression frequencies are generated by programmed frequency divisions effected in parallel from a standard frequency and applied to two mixers. The first mixer further receives the frequency from the preceding decade and is followed by a divide-by-2 divider, whereas the second mixer is further receives the output of said divider and is followed by a divide-by-5 divider.

Description:
BACKGROUND OF THE INVENTION 
     In U.S. Pat. No. 4,008,443 filed by the Applicant on June 27, 1974, an iterative frequency synthesizer has been described whose basic element is a &#34;quaternade&#34;, that is to say means for inserting a local frequency increment insertion means comprising a variable frequency taking on, in any order, one of four arithmetic progression values. 
     To construct a &#34;quaternary&#34; synthesizer, i.e. supplying the frequency to be synthesized by generating, in its different successive stages, significant digits of the number which expresses this frequency in the 4 base numeration system, it is sufficient for each stage to comprise a mixer providing a beat between the frequency from the preceding stage and a local variable frequency incremented by the four above mentioned arithmetic progression values. 
     If the mixing is additive, the local frequency must comprise a fixed part three times that of the input frequency of the stage. 
     If the mixing is subtractive, the local frequency must comprise a fixed part five times that of the input frequency of the stage. 
     In both cases it is sufficient to divide the frequency from the mixer by 4 so as to bring its fixed part to the same value at the output of the different stages. 
     According to an important feature of the above mentioned patent, the generation of the four arithmetic progression frequency values is provided from a single standard frequency, by dividing the standard frequency by fixed ratios which may take on at least two different values depending on the code which programs the synthesizer and selecting harmonics of the frequencies resulting from these divisions. 
     In the embodiment described in the above mentioned patent, two such divisions are effected in series, the first with two values of the rate and the second with four values. 
     SUMMARY OF THE INVENTION 
     A first object of the present invention is to simplify the harmonic filtering. This result is obtained by effecting two parallel divisions, each with two values of the divider ratio and by mixing the two frequencies thus obtained, which may take on two values each. 
     A second object of the invention is to do away with the need to generate harmonics, so as to avoid the use of a multiplier. 
     This result is obtained by effecting two parallel divisions, each with two values of the divider ratio, starting from two separate standard frequencies. 
     The basic element has been used, in the embodiments described in the above mentioned patent, for constructing a quaternary synthesizer. 
     The invention proposes using it for forming a decimal synthesizer. 
     For this purpose, according to another feature of the invention, each decade of the synthesizer is formed by two cascade connected elements, the first of which comprises a mixer which provides a beat between the frequency from the preceding decade and a local frequency taking on, depending on the programming code, values taken from a first set of four arithmetic progression values, said mixer being followed by a divide-by-two divider and in which the second element comprises a mixer which provides the beat between the frequency from the first element and a local frequency taking on, depending on the programming code, values taken from a second set of four arithmetic progression values, followed by a divide-by-five divider, and means for selecting, from the sixteen programming codes which define all the possible combinations of the two sets of four values, the ten codes which determine the generation of ten arithmetic progression output frequencies with a frequency step equal to a tenth of the total increment of the decade. 
     In a preferred embodiment, the four possible ratio values of the dividers which each decade comprises are programmed from ten codes selected from their sixteen possible programming codes by converting these latter from the code 1-2-4-8 into a code 1-2-2-4. 
     In a particularly simple embodiment, the two sets of values are identical, the first of these values being three times the fixed part of the frequency from the preceding stages. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will be clear from the following description. 
     In the accompanying drawing: 
     FIG. 1 is the diagram of a basic quaternary generator for forming a decimal synthesizer decade in accordance with a first preferred embodiment of the invention; 
     FIG. 2 shows said decade; 
     FIG. 3 shows a &#34;quaternade&#34; according to another embodiment; 
     FIG. 4 shows a logic code conversion circuit used with the quaternade of FIG. 3; and 
     FIG. 5 illustrates one embodiment of a quaternary synthesizer using such a quaternade. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1 is shown the generation of a frequency capable of taking on any one of four arithmetic progression values 24A, 25A, 26A and 27A, depending on the programmed variable division ratios of two dividers D1 and D3 supplied with a standard frequency of 24A. 
     In such a circuit, A is the smallest frequency increment which a synthesizer formed from the basic element shown may generate. 
     Division of 24A by two or by three in D1 gives the values 12A and 8A, divided by two in a fixed divider D2 to give 6A or 4A. This first frequency 6A or 4A is filtered by the band pass filter FL1 and is applied to a mixer Me. 
     A second frequency, also applied to Me after filtering by FL2, takes on the values 20A or 21A obtained by dividing 24A by 3 or 4, by dividing the result by 2 in a fixed divider D4 and by forming the harmonic 5 of frequency 4A and the harmonic 7 of frequency 3A in a multiplier Mu. 
     It will be noted that, in the solution which has just been described, the filtering problems are very simple to resolve, because the frequencies to be eliminated are far from the necessary pass band for filter FL3. 
     A first and a second frequency taking on the whole of values 24A-25A-26A-27A are applied respectively to the mixer M1 of a first component element of the decade shown in FIG. 2 and to the mixer M2 of a second element in series with the first one. It should be well understood that two quaternary generators such as the one shown in FIG. 1 are required, for though the two assemblies are identical, the values selected by the program of this synthesizer for synthesizing any given frequency are not identical. 
     Since the decade illustrated is assumed to occupy any rank i in the synthesizer, its input frequency comprises a carrier Fo here equal to 8A, for example and an increment Δi. The additive beat with the frequencies 24A to 27A, filtered by FL3, gives frequencies (32A to 35A) +Δi which division by 2 in D5 brings down to (16A+17.5A)+Δi/2. 
     The beat between this frequency and the frequency 24A to 27A in M2, filtered by FL4, gives a frequency (40A to 44.5A)+Δi/2 which, after being divided by 5 in D6, gives (8A to 8.9A)+Δi/10. 
     The table below shows the set of output frequencies Fs (not taking into account the term Δi/10) for the possible different values of the frequencies F1 and F2 applied respectively to M1 and M2 from quaternary generators: 
     
         ______________________________________F1   F2    Fs     N°                  1-2-4-8     1-2-2-4______________________________________24   24    8      025   24    8.1    1    X                 X26   24    8.2    2        X                 X27   24    8.3    3    X   X             X        X24   26    8.4    4             X                     X25   26    8.5    5    X        X        X            X26   26    8.6    6        X    X            X        X27   26    8.7    7    X   X    X        X   X        X26   27    8.8    8                 X        X    X   X27   27    8.9    9    X            X    X   X    X   X24   25    8.2    10       X        X25   25    8.3    11   X   X        X26   25    8.4    12            X   X27   25    8.5    13   X        X   X24   27    8.6    14       X    X   X25   27    8.7    15   X   X    X   X______________________________________ 
    
     In the table have been shown the numbers, going from 0 to 15, of the sixteen possible combinations of the codes for programming the dividers of said generators and the translation of these numbers into BCD code 1-2-4-8 and into the code 1-2-2-4. 
     Since the programming computer of the synthesizer which calculates the codes for each desired value of Fs, supplies said codes in BCD, it is sufficient to convert them into the code 1-2-2-4 in order to eliminate the six redundant combinations. A converter circuit, formed from two OR gates, is illustrated in FIG. 4. 
     The &#34;quaternade&#34; illustrated in FIG. 3 uses two standard frequencies, 33.6A and 32A in the example described, which are divided respectively by 6 or 7 and by 5 or 8 in the dividers D7 and D8 so as to give, after filtering in FL5, four values 4A; 4.8A; 5.6A; and 6.4A. 
     Diodes d1 and d2 provide transmission of the signal from that one of the two dividers which is active for a code considered. 
     The purpose of filter FL5 is here solely to eliminate the parasite harmonics generated by dividers D7 and D8. 
     By way of example of application of such a &#34;quaternade&#34;, in FIG. 5 is shown a 94.8 to 98.8 MHz synthesizer comprising four identical quaternades Q1, Q2, Q4, and Q5, in which the generator of four arithmetic progression frequency values is identical to the one shown in FIG. 3 and an output quaternade Q5 which is distinguished from the preceding ones by the absence of divider D9. 
     Three standard frequencies are used, namely: 32 MHz and 33.6 MHz, which are applied to dividers D7 and D8 of each quaternade and 67.1 MHz. 
     This latter is, on the one hand, applied to a mixer M3 which also receives the output frequency from FL5 (taking on the values 4, 4.8, 5.6 and 6.4 MHz as explained above), and on the other hand to a mixer M5 which further receives a frequency of 4 MHz obtained by division of the 32 MHz frequency in divider D10. The additive 71.1 MHz beat is filtered in FL8, then divided by three in a divider D11 to give a frequency of 23.7 MHz. This latter frequency, after filtering in FL6, is mixed in M4 with the additive beat in M3, filtered in FL8, between the frequency from FL5 and standard frequency of 67.1 MHz. 
     The frequency from M4, after filtering in FL7, is divided by four in D9 and applied to the following quaternade. Thus, the four values 94.8 MHz; 95.6 MHz; 96.4 MHz and 97.2 MHz are obtained which, after being divided by four, give 23.7; 23.9; 24.1 and 24.3 MHz. 
     In the second quaternade Q2 there is obtained, for each of the above frequencies 23.7; 23.9; 24.1 and 24.3 MHz, four frequencies the last of which (24.9 MHz) for those which correspond to 24.3 MHz, will be eliminated by FL6. 
     Similarly, for each of the the fifteen output frequencies from Q2, there will be obtained at the output of Q3 four frequencies of which those which exceed 24.7 MHz will be eliminated by FL6. Finally, since the last quaternade Q5 does not comprise any divide-by-4 divider D9, frequencies will be obtained at its output varying from 94.8 to 90.8 MHz. 
     It goes without saying that the circuits described and illustrated may be modified, without departing from the spirit of the invention.