JPH0251299B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency synthesizer, in particular:
Frequency synthesizer using phase locked loop (PLL) (including general cover receiver oscillator and spectrum analyzer)
Regarding.

Conventionally, various frequency synthesizers using a phase-locked circuit PLL have been proposed, as shown in FIGS.
However, there is a problem in that the frequency can only be controlled at intervals of the reference frequency i.

Symbol a in Figures 1a to d indicates the reference frequency oscillator (OSC), and b indicates the phase comparator (φ/
D), c is a low pass filter (LPF), d is a voltage controlled oscillator (VCO), e is a frequency divider (1/N, 1/
M), e' is a prescaler (1/p), g is a frequency multiplier (xM), h is a frequency mixer (mixer), and i is a local frequency oscillator (local oscillator).

Therefore, if the reference frequency i is lowered, control can be performed at finer frequency intervals.

However, if you want to change the frequency suddenly, the response speed becomes an issue, so the reference oscillation frequency must be set as high as possible, and the desire to lower the reference frequency and the desire to increase the response speed are compatible. It becomes contradictory.

In other conventional synthesizers, the reference frequency from the oscillator (OSC) a is set to 10K, as shown in Figure 2.
Hz, and in order to create minute steps, it is possible to obtain a 10Hz step by using a 1/1000 frequency divider e for the output of the voltage controlled oscillator d. In this case, N of the 1/N frequency divider e should be set to 400~ 499, the output is
It will be 4.00~4.99KHz.

However, as it is, the output frequency is very low, so it is difficult to use it in a high frequency synthesizer.

Therefore, for example, a frequency mixer j that handles oscillations in units of 10Hz and 100Hz, a frequency mixer j that handles oscillations in units of 1KHz and 10KHz, and a frequency mixer j that handles oscillations in units of 1KHz and 10KHz, and
The desired frequency is obtained using a frequency mixer j that handles oscillations in units of 1MHz and 10MHz, respectively.As shown in Figure 3, the output from frequency mixer j is ( ₁ + ₂ ). Two frequencies ( ₁ − ₂ ) appear.

When obtaining minute steps using a PLL with a high reference oscillation frequency, the output will be at a low frequency as in the example above, resulting in ( ₁ + ₂ ) and ( _1
−2 ) become close to each other.

Therefore, it is necessary to connect a filter to the output, and it is difficult and complicated to adjust the cut-off frequency of the filter.

The present invention aims to solve these problems and provides a frequency synthesizer, such as a wideband frequency synthesizer, that can realize minute step changes with a simple configuration and that can reduce costs. With the goal.

For this reason, the frequency synthesizer of the present invention has a reference frequency oscillator that outputs a reference frequency signal, and a frequency synthesizer that receives the reference frequency signal from the reference frequency oscillator and has the same frequency and a phase difference of 90 degrees.
It is equipped with a phase converter that outputs two reference frequency signals, a microstep frequency signal generator that outputs a microstep frequency signal, and a microstep frequency signal generator that receives step frequency signals from the microstep frequency signal generator to generate the same frequency and mutual 2 where the phase difference is 90°
a delay circuit that outputs two step frequency signals;
first and second filters each receiving each step frequency signal from the delay circuit and outputting a sine wave signal; one of the reference frequency signals with an advanced phase and one of the sine wave signals with a slow phase; a first balanced modulator that receives and performs modulation, and a second balanced modulator that receives and modulates a slower phase of the reference frequency signal and an advanced phase of the sine wave signal. and the output ends of the first and second modulators are connected to the output terminals, respectively.

Generally, a frequency mixing circuit is used to synthesize frequencies, but with a normal mixing circuit, unintended frequencies such as image frequencies and leakage of input frequencies occur, making it impossible to obtain a pure output. In particular, if the image frequencies are close to each other, it is difficult to remove them.

In order to improve this, the frequency synthesizer of the present invention uses first and second balanced modulators (balanced modulation circuit) and a phase converter (phase shift circuit) for frequency mixing as described above. .

The first and second balanced modulators are
The balanced characteristics of each can cancel input frequency leakage.

Furthermore, since only one balanced modulator produces an image frequency, in order to eliminate this, the frequency synthesizer of the present invention adds another balanced modulator and a phase converter to cancel out the image frequency. This allows the output to have the desired frequency with high purity.

The sum of the outputs of the two balanced modulators described above is a composite output of the minute step frequency and the step frequency, and becomes a highly pure single frequency with the image frequency canceled.

Note that the reference frequency in this specification refers to a frequency used as a base for each step frequency generation circuit.

To make a microstep frequency synthesizer,
It is necessary to mix a plurality of frequencies, and the present invention improves the mixing circuit.

Note that a balanced modulator is a circuit that obtains output frequencies ₁ - ₂ and ₁ + ₂ for input frequencies ₁ and ₂ , and since the inputs are balanced, there is little leakage of input frequencies.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a block diagram showing the main parts of a frequency synthesizer as a first embodiment of the present invention, and FIGS. 5 to 10 are block diagrams of a second embodiment of the present invention. This shows a specific example of a frequency synthesizer as an example. Figures 5 and 6 are block diagrams and electrical circuit diagrams of the specific example of the present invention, respectively, and Figures 7 and 8 are respective diagrams of the specific example of the present invention.
9 and 10 are block diagrams and electrical circuit diagrams of the PLL main blocks, respectively.

As shown in FIG. 4, in the first embodiment, a reference frequency oscillator 1 is provided, and the reference frequency ₁ (=10MHz) from this oscillator 1 is transmitted to the phase converter 2.
are converted into voltages v ₁ and v ₁ ' having a phase difference of 90° from each other, and sent to balanced modulators 3a and 3b.

It can also be used as a minute step frequency signal generator.
A 10KHz step synthesizer 4 is provided, and the frequency ₂ (=4.00
~4.99MHz) is passed through a 1/250 frequency divider 5 to a D-flip-flop 6a as a delay circuit.
6b, this D-flip-flop 6
The signals with a phase difference of 90° in a and 6b pass through filters 7a and 7b and become voltages v ₂ and v ₂ ', respectively, and are sent to a balanced modulator (second modulator) 3b and a balanced modulator, respectively. The signal is sent to the modulator (first modulator) 3a.

90° phase difference between each voltage v ₁ and v ₁ ′ and each voltage v ₂ ,
The following equation holds due to the 90° phase difference with v ₂ ′.

v ₁ =V ₁ cosω ₁ t v ₁ ′=V ₁ cos(ω ₁ t+π/2) =V ₁ sinω ₁ t v ₂ =V ₂ cosω ₂ t v ₂ ′=V ₂ cos(ω ₂ t+π/2) =V ₂ sinω ₂ t Each of these voltages enters the balanced modulators 3a and 3b, and the output thereof is v _B =v ₁ ×v ₂ ′=V ₁ cosω ₁ t・V ₂ sinω ₂ t v _B ′=v ₁ ′× v ₂ =V ₁ sinω ₁ t・V ₂ cosω ₂ t.

These signals are combined by connecting the output sides of the balanced modulators 3a and 3b, and v=v _B +v _B ′ =V ₁ V ₂ cosω ₁ t・sinω ₂ t +V ₁ V ₂ sinω ₁ t・cosω ₂ t =V ₁ V ₂ sin(ω ₁ +ω ₂ )t.

As can be seen from this equation, only the (ω ₁ +ω ₂ ) component, that is, the upper sideband, appears due to the phase shift network.

Here, ₁ = ω ₁ /2π = 10MHz, ₂ = ω _{2 /2π} = 4.00KHz ~ 4.99KHz, so the output is ( ₁ + ₂ ) = 10.00400MHz ~
10.00499MHz will be obtained.

In addition, the frequency of the difference between reference frequency ₁ and minute step frequency ₂ ( ₁ − ₂ ) = 9.99600MHz to 9.99501M
Hz does not appear at all due to the above configuration.

As shown in FIGS. 5 to 10, in the second embodiment,
Terminals T ₁ to _{T 12} in each figure are connected to each other, and in FIGS. 5 to 10, the same reference numerals as in FIGS. 1 to 4 indicate substantially the same components.

As shown in FIGS. 5 and 6, the frequency synthesizer block inputs and outputs each frequency through terminals T ₁ -T ₃ and T ₇ .

Terminal T ₁ : 4.00 to 4.99KHz input terminal from PLL sub-block T ₂ : 4.00 to 4.99KHz input terminal with a phase difference of 90 degrees from the input from terminal T ₁ T ₃ : 400 to 499KHz input terminal from PLL sub-block T ₇ : 30.00000~30.09999MHz output, goes to mixer of PLL main block. In addition, symbol 7c in Fig. 5 indicates a low pass filter (LPF), 8 indicates an amplifier (AMP), and 9
indicates a frequency mixer (MIX), and 10 indicates a bandpass filter (BPF).

As shown in FIGS. 7 and 8, the PLL sub-block performs input/output of each frequency and BCD (binary coded decimal) input for frequency setting through terminals _T1 to _T6 .

Terminal T ₁ : Output from 4.00 to 4.99KHz (10Hz step) Terminal T ₂ : Has a phase difference of 90° from the input from terminal T ₁
4.00~4.99KHz output (10Hz step) Terminal _T3 : 400~499KHz output (1KHz step) Terminal _T4 : 2-digit BCD input terminal for frequency setting (0~99KHz) _T5 : Frequency setting (0 to 990KHz) 2-digit BCD input terminal _T6 : Input reference oscillation (40KHz) In addition, the symbol 5' in Fig. 7 indicates a frequency divider, and 11 indicates a phase comparator. , 12 is a frequency divider, 13 is a low pass filter (LPF), and 14 is a voltage controlled oscillator (VCO).

As shown in Figs. 9 and 10, the PLL main block has a reference oscillator 4 which is the final output.
This oscillator 4 determines the overall performance.

Terminal T ₆ : 40KHz reference oscillation is supplied to the PLL sub-block Terminal T ₈ : 2-digit BCD input terminal for setting the frequency (0 to 9.9MHz) T ₉ : Switching the frequency setting (50, 60, 70MHz) Terminal T ₁₀ : Final output (50.00000~79.99999MHz,
4V _pp ) Terminal T ₁₁ : VCO switching (If 9V is applied here, it will oscillate.) Terminal T ₁₂ : VCO switching (If 9V is applied here, it will oscillate.) In addition, code 15 in Figure 9 is a level converter. ,1
6 indicates a buffer amplifier, respectively.

In this way, in the second embodiment, the _minute step frequency (50.00000~
79.99999MHz), and the other effects of the second embodiment are almost the same as those of the first embodiment.

The frequency synthesizer of the present invention can be used as a frequency synthesizer application device, and if the frequency is adjusted and used as a local oscillator for a receiver with an intermediate frequency of 50 MHz, the frequency synthesizer of the present invention can provide a so-called general coverage of the receiving frequency of 0 to 30 MHz. A receiver can be created.

Furthermore, by using a microcomputer for frequency control, you can make program reservations, search functions, and automatically call up all kinds of broadcast stations.
When combined with a transmitter, an unmanned radio station is also possible.

Furthermore, by using a frequency synthesizer, a spectrum analyzer can be created that can be used by simply pressing a key switch.

As described in detail above, according to the frequency synthesizer of the present invention, there is a reference frequency oscillator that outputs a reference frequency signal, and a reference frequency signal received from the reference frequency oscillator has the same frequency and a phase difference of 90 degrees. It is equipped with a phase converter that outputs two reference frequency signals of .degree., a microstep frequency signal generator that outputs a microstep frequency signal, and a step frequency signal that receives a step frequency signal from the microstep frequency signal generator and outputs a microstep frequency signal of the same frequency. and a delay circuit that outputs two step frequency signals with a phase difference of 90 degrees from each other, and first and second filters that receive each step frequency signal from the delay circuit and output a sine wave signal. a first balanced modulator that receives and modulates a phase-advanced one of the reference frequency signals and a slow-phase one of the sine wave signals; a second balanced modulator that receives and modulates the phase-advanced one of the sine wave signals, and the output ends of the first and second balanced modulators are connected to the output terminals, respectively. With this simple configuration, the following effects and advantages can be obtained.

(1) Since the component of frequency ( ₁ − ₂ ) does not appear in the composite frequency, minute step frequency ₂ can be set to a fairly low frequency.

(2) Since the frequency of the voltage controlled oscillator can be relatively low, a CMOS type IC can be used in the circuit, reducing power consumption, and the circuit does not need high-frequency components. This makes it possible to reduce the size and cost.

(3) Since there is no need for expensive and difficult-to-adjust filters, miniaturization and cost reduction are also possible.

(4) The reference frequency can be lowered and the response speed can be increased.

(5) Since two balanced modulators and a phase modulator are used, the image frequency is removed and the desired frequency can be obtained with high purity in the output.

[Brief explanation of drawings]

Figures 1a to d and Figure 2 are all block diagrams of a frequency synthesizer using a conventional phase-locked circuit PLL, Figure 3 shows a frequency mixer, and Figure 4 shows the first embodiment of the present invention. FIG. 5 is a block diagram showing the main parts of a frequency synthesizer as an example, and FIGS. 5 to 10 show specific examples of a frequency synthesizer as a second embodiment of the present invention, and FIGS. The block diagram and electrical circuit diagram for the part, Figures 7 and 8 are the PLL respectively.
9 and 10 are the block diagram and electrical circuit diagram of the PLL main block, respectively. 1... Reference frequency oscillator (OSC), 2... Phase converter, 3a... Balanced modulator as a first modulator, 3b... Balanced modulator as a second modulator,
4... As a minute step frequency signal generator
10KHz step synthesizer, 5,5'...
1/250 frequency divider, 6a, 6b...D-flip-flop as a delay circuit, 7a...first filter (LPF), 7b...second filter (LPF),
7c...Low pass filter, 8...Amplifier, 9...
...Frequency mixer (MIX), 10...Band pass filter (BPF), 11...Phase comparator, 12...
Frequency divider, 13...Low pass filter (LPF), 1
4... Voltage controlled oscillator (VCO), 15... Level converter, 16... Buffer amplifier.

Claims (1)

[Claims] 1. A reference frequency oscillator that outputs a reference frequency signal, and a phase converter that receives the reference frequency signal from the reference frequency oscillator and outputs two reference frequency signals of the same frequency and with a phase difference of 90 degrees. A minute step frequency signal generator that outputs a minute step frequency signal, and two steps that receive step frequency signals from the same minute step frequency signal generator and have the same frequency and a phase difference of 90 degrees. a delay circuit that outputs a frequency signal; first and second filters that receive each step frequency signal from the delay circuit and output a sine wave signal; a first balanced modulator that performs modulation in response to a reference frequency signal with a slow phase; a first balanced modulator that receives a slow phase of the reference frequency signal and an advanced phase of the sine wave signal; A frequency synthesizer, characterized in that a second balanced modulator for performing modulation is provided, and output terminals of the first and second balanced modulators are connected to output terminals, respectively.