SU761930A1 - Precision-type frequency comparator - Google Patents

Description

The invention relates to electronics and can be used to accurately compare frequencies.

Known frequency comparators containing a switch, keys, a switching signal generator, capacitor converters and low-pass filters [13.

A disadvantage of the known devices is that they have a low conversion coefficient. The steepness of the frequency response of these comparators depends on the absolute magnitude of the frequencies being compared. In addition, they have a high level of internal interference. fifteen

The closest in technical essence to the proposed device is a device containing a key block, a trigger connected in series and a lower-frequency filter [20}.

A disadvantage of the known device is low sensitivity.

The purpose of the invention is to increase sensitivity. 25

This goal is achieved by the fact that in the device containing the key block, the trigger and the low-pass filter connected in series, a shaper of duration, serially connected switching frequency divider, a switch, a period shaper whose output is connected to the first input of the trigger, the second input of which is connected to the output of the driver for the duration / input of the latter is connected to the output of the key block, the first input of which is connected to the second output of the switch, and the second input of the key block is connected to the input of the filter zhnih frequency divider and to the input of the switching frequency.

In FIG. Fig. 1 shows a block diagram of the device; Fig. 2 - waveforms of pulses in different parts of the device Cu ?, - signal of the compared frequency Φΐ; ΙΙρ ^ - signal of comparable frequency Ф2; υ _{ϊί> Μχ the} output signal of the pulse period former; ^and 4b "is the output of the trigger;

“Pulse shaper output signal).

The device comprises a switch 1, a period former 2, a key block 3, a duration former 4, a trigger 5, a low-pass filter b and a switching frequency divider 7.

The device operates as follows.

'761930.

The pulses of the signals P ₁ and P _g are fed to the inputs of the switch 1. When a signal is supplied to the control input of the switch, the frequency P _g goes to the shaper 2, and P ^ to the input of the block 3. If there is no signal at the control input, it is vice versa. ''

Assume that at first there is no signal at the. · / Control input. In this case, the frequency P? arrives at shaper 2, and G, at the input ₍ block 3, which, suppose, is closed. Then, pulses are generated at the output of shaper 2 (fig.2b).

The period of these pulses is equal to K _g / R _g , the Negative front of it flips trigger 5 and a signal appears opening it at the input of block 3 .15.

In this case, the shaper 4 generates a pulse duration, which is equal to ac = Kd / b. After the formation of the pulse, the trailing edge () 20 overturns the trigger 5 and block 3 closes. Then, with the arrival of the next pulse of the signal (1¾), the process repeats. The constant component of the signal is rive and, = and _pct .

Cd ^

The pulses of sludge, 5duh arrive at the input of the divider 7 of the formation of the switching signal. In the initial position, the polar-absence of a signal at the output of this divider. After the passage of the pulses, a signal appears at the output of the divider, which sets the switch 1 to the position when the frequency P · »arrives at the input of the former 2. In this case, the constant component of the signal will be equal to _r = and _pit KdR ·, / P _G K, .

The input of the filter 6 thus receives packets of pulse numbers with different constants; 40 in each interlaced packet.

The difference between the constant components will be equal to - and _pm t. <A) ·

Thus, at the output of filter 6, an envelope signal of pulse packets is generated, the amplitude of which is proportional to the frequency difference, 50 and the phase determines the sign of the difference in the frequency. Transforming, we have

With small detunings, we can assume that = = 2 and _pt (k ₅ / k _g Φ, ( _{г g} Ф F,), i.e., the frequency response has high linearity and its shape does not depend on the parameters of the analog elements of the device.

The proposed device has, in comparison with the known, a higher conversion coefficient (gain 6-8. Times), high stability - the shape of the frequency response and independence of the characteristics of the parameters. From the parameters of the elements, a smaller amount of internal interference (5-6 times), as well as the complete absence of analog time-consuming elements in the device, which makes it possible to fabricate the device on logic elements and, thus, favors microminiaturization.

Claims (1)

Claim A precision frequency comparator containing a block of keys, a trigger connected in series and a low-pass filter, distinguishing with the fact that, in order to increase sensitivity, a shaper of duration, serially connected switching frequency divider, switch, period former, the output of which is connected to the first input of the trigger, the second input of which is connected to the output of the shaper of duration, the input of the latter is connected to the output of the key block, the first input of which is connected to the second output of the comm : tator, and the second input of the key block is connected to the input of the low-pass filter and to the input of the switching frequency divider.