Description:TECHNICAL FIELD
[0001] The present disclosure relates to a frequency sensing circuit. More particularly the present disclosure relates to a circuit for sensing a frequency of an input signal, in a frequency band, of an RF subsystem.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] For conventional software defined radios operating in VUHF bands, the bandwidths are in the multioctave range. As the bandwidth of operation is very broad, designing different stages of RF amplification and filtering becomes complicated. It requires designing of RF circuits for unrealizable broad bands. In Amplifiers the challenge is achieving harmonic rejection throughout the band when the harmonics of lower frequencies are already there in the band of operation. This kind of designs requires switched RF circuit banks, which consist of a switches and RF circuits integrated to a single module. They usually consist of an input switch, followed by the RF circuit for each channel of the switch followed by an output switch. Integrating the circuits using switches in a module eliminates transition between circuits, providing optimum matching, insertion loss or gain, flatness, VSWR and overall better performance of the device. The use of internal channelization allows for optimum rejection and isolation in filters.
[0004] In broadband power amplifiers for achieving harmonic suppression designers have to design multiple narrowband matching or filter networks together with input and output switch to meet the harmonic specification at those narrow bands. The narrow bands are to be planned in such a way that the second and third harmonics of any frequency point in that band does not come in the same band. These designs need to be selected based on the frequency of signal being sent to the power amplifier after modulation. In a power amplifier module using frequency sensing the circuit can enable the corresponding RF network before enabling the Power amplifier. This makes the high-power amplifier ready with its load condition before it is DC biased to ON. If there is no load circuit turned ON before setting the operating point of high-power amplifier, it will be loaded with an open load at turn ON.
[0005] Presently in Radio transmitters the frequency representing word is also fed as an additional input together with the RF input to select the band of switched filter or matching network bank of the power amplifier module. With the addition of frequency sensing feature in transmitters the band selection of antenna switching units and switched filter or matching network bank can be done in the RF level itself. If the controls of switched filter bank change or reset from the controls input from the baseband card the PA will be exposed to an open load and it will cause damage to the Amplifier. In case of control failure, the PA sequencing can be configured accordingly to protect the PA.
[0006] If there is onboard sensing, the RF input will be passing to the subsequent stages only after the stages are ready with bias. This enables designers to design switched narrowband filters, matching networks, driver, Amplifiers or attenuator to meet performance criteria in required application for which the switch will be enabled based on the frequency of the input. In amplifiers if there are any frequency dependent observation like power, IMD etc the operating point can be modified accordingly as there is an identifier for frequency.
[0007] In antenna switching units where one among multiple antennas will be selected using switches based on the frequency band. So broadband transmitting antenna with less gain at the band edges can be replaced by narrow band antennas with flat gain throughout the band selected using frequency dependent switches. The input of the antenna will be sampled and the antenna to transmit will be selected based on the detected frequency band.
[0008] There is, therefore, a need for a frequency sensing circuit for identifying the frequency of input applied to it, and the same through microcontroller interface can be used for controlling multiple frequency dependent parameters of the broadband RF circuits.

OBJECTS OF THE PRESENT DISCLOSURE
[0009] Some of the objects of the present disclosure, which at least one embodiment herein satisfy are as listed herein below.
[0010] It is an object of the present disclosure to provide a circuit for sensing a frequency of an input signal of RF band, which allow frequency sensing of the high frequency signals.
[0011] It is an object of the present disclosure to provide a circuit for sensing a frequency of an input signal of RF band, which allow auto switching of the RF networks based on the sensed frequency.
[0012] It is an object of the present disclosure to provide a circuit for sensing a frequency of an input signal of RF band, which allow designer to design switched RF networks with subsystems such as narrowband filters, matching networks, driver, amplifier or attenuators to meet required criterion of the application.

SUMMARY
[0013] The present disclosure relates to a frequency sensing circuit. More particularly the present disclosure relates to a circuit for sensing a frequency of an input signal, in a frequency band, of an RF subsystem
[0014] An aspect of the present disclosure pertains to a circuit for sensing a frequency of an input signal, in a frequency band, of an RF subsystem. The circuit includes a pre-scaler circuit configured to receive the input signal, and the pre-scaler circuit is configured to divide the frequency of the input signal. An error detection circuit configured to receive an output of the pre-scaler circuit, and configured to generate an error signal based on comparison between a reference frequency and each of the plurality of samples. A charge to voltage converting circuit configured to receive the error signal and outputs a voltage signal proportional to the error signal. A differential amplifier circuit having a first input coupled to an output of the charge to voltage conversion circuit and a second input configured to receive a reference voltage signal, and the differential amplifier is configured to output a voltage corresponding to a frequency within the frequency band. Power supply voltages of the differential amplifier are corresponding to a lower frequency edge and an upper frequency edge of the frequency band.
[0015] In an aspect, the pre-scaler circuit may comprise a frequency divider.
[0016] In an aspect, the error detection circuit may comprise any or combination of a phase frequency detector, and a charge pump.
[0017] In an aspect, the charge to voltage converting circuit may comprise a charge to voltage amplifier.
[0018] In an aspect, the reference frequency may be different that a pre-scaled frequency of the plurality of samples for avoiding any occurrence of blank pulses at the output of error detection circuit.
[0019] In an aspect, the reference voltage signal may correspond any of a lowest or a highest value of the output of the charge to voltage conversion circuit.
[0020] In an aspect, a gain of differential amplifier circuit may correspond to dynamic range V1 to V2 where V1 and V2 are the minimum and maximum output voltage levels).
[0021] In an aspect, the frequency of the input signal may be in a range F1 to F2 (where F2 is greater than F1).
[0022] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF DRAWINGS
[0023] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The diagrams are for illustration only, which thus is not a limitation of the present disclosure.
[0024] In the figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.
[0025] FIG. 1 illustrates an exemplary representation of a circuit for sensing a frequency of a RF inputs signal, in accordance with an embodiment of the present disclosure.
[0026] FIG. 2 illustrates an exemplary implementation of the proposed circuit for sensing a frequency of a RF inputs signal in RF network, in accordance with an embodiment of the present disclosure.
[0027] FIGs. 3A-B illustrates exemplary interface circuit used in the FIG. 2, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0028] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosure as defined by the appended claims.
[0029] In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without some of these specific details.
[0030] The present disclosure relates to a frequency sensing circuit. More particularly the present disclosure relates to a circuit for sensing a frequency of an input signal, in a frequency band, of an RF subsystem.
[0031] The present disclosure elaborates upon a circuit for sensing a frequency of an input signal, in a frequency band, of an RF subsystem. The circuit includes a pre-scaler circuit configured to receive the input signal, and the pre-scaler circuit is configured to divide the frequency of the input signal into a plurality of samples. An error detection circuit configured to receive an output of the pre-scaler circuit, and configured to generate an error signal based on comparison between a reference frequency and each of the plurality of samples. A charge to voltage converting circuit configured to receive the error signal and outputs a voltage signal proportional to the error signal. A differential amplifier circuit having a first input coupled to an output of the charge to voltage conversion circuit and a second input configured to receive a reference voltage signal, and the differential amplifier is configured to output a voltage corresponding to a frequency within the frequency band. Power supply voltages of the differential amplifier are corresponding to a lower frequency edge and an upper frequency edge of the frequency band.
[0032] In an embodiment, the pre-scaler circuit can comprise a frequency divider.
[0033] In an embodiment, the error detection circuit can comprise any or combination of a phase frequency detector, and a charge pump.
[0034] In an embodiment, the charge to voltage converting circuit can comprise a voltage amplifier.
[0035] In an embodiment, the reference frequency can be different that a pre-scaled frequency of the plurality of samples for avoiding any occurrence of blank pulses at the output of error detection circuit.
[0036] In an embodiment, the reference voltage signal can correspond any of a lowest or a highest value of the output of the charge to voltage conversion circuit.
[0037] In an embodiment, a gain of differential amplifier circuit can correspond to dynamic range V1 to V2 (where V1 and V2 are the minimum and maximum output voltage levels).
[0038] In an embodiment, the frequency of the input signal can be in a range F1 to F2 (where F2 is greater than F1).
[0039] FIG. 1 illustrates an exemplary representation of a circuit for sensing a frequency of a RF inputs signal, in accordance with an embodiment of the present disclosure.
[0040] FIG. 2 illustrates an exemplary implementation of the proposed circuit for sensing a frequency of a RF inputs signal in RF network, in accordance with an embodiment of the present disclosure.
[0041] FIGs. 3A-B illustrates exemplary interface circuit used in the FIG. 2, in accordance with an embodiment of the present disclosure.
[0042] As illustrated a circuit 100 for sensing a frequency of an input signal, in a frequency band, of an RF subsystem can include a pre-scaler circuit 102 that can be configured to receive the input signal, and divide the frequency of the input signal into a plurality of samples. The frequency of the input signal can be between 1MHz to Ku band. The pre-scaler circuit 102 is following either coupled arm of directional coupler or any one output of power divider. The pre-scaler circuit 102 can has a scaling factor of N. The input signal can be passed through the pre-scaler circuit 102 and an output of the pre-scaler circuit can be same in amplitude but divided by N in frequency of the input signal. The division of the input signal frequency is done in such a way that a pre-scaled frequency, after division, of a plurality of samples is comparable to the reference frequency.
[0043] An error detection circuit 104 that can be electrically configured with the pre-scaler circuit 102 to receive an output of the pre-scaler circuit 102. The error detection circuit104 can be configured to generate an error signal based on comparison between a reference frequency and each of the plurality of samples. The error detection circuit 104 can include any or combination of a phase frequency detector and a charge pump, and the reference frequency can be different that a pre-scaled frequency of the plurality of samples for avoiding any occurrence of black pulses at the output of error detection circuit. The error detection circuit 104 can compare the output of the pre-scaler circuit 102 with the fixed reference frequency in order to generate a correction voltage or error voltage signal. If not mentioned the polarity of phase to frequency detector is positive. The reference frequency can be less than the pre-scaled frequency of the plurality of samples of the frequency band. In general, the reference frequency remains constant and the frequency out of pre-scaled plurality of samples changes. So, when the frequency of the input signal changes a pulse width at the output of the charge pump of keeps increasing or decreasing based on the decrease or increase of input signal frequency.
[0044] In an embodiment, the circuit 100 can include a charge to voltage converting circuit 106 that can be electrically configured with the error detection circuit 104 to receive the error signal and outputs a voltage signal proportional to the error signal. The charge to voltage converting circuit can include but is not limited to a charge amplifier. The charge to voltage circuit 106 can be an electronic integrator that can produce a voltage output proportional to integrated value of input current. The charge to voltage converting circuit 106 can offset the input current using a feedback reference capacitor and can produce an output voltage proportional to the value of reference capacitor but proportional to a total input charge flowing during the specified time period. The gain of the circuit can be determined by the value of the feedback capacitor.
[0045] In an embodiment, the circuit 100 can include a differential amplifier circuit 108 having a first input that can be electrically coupled with an output of the charge to voltage conversion circuit 106 and a second input configured to receive a reference voltage signal. The differential amplifier is configured to output a voltage corresponding to a frequency within the frequency band. Power supply voltages of the differential amplifier are corresponding to a lower frequency edge and an upper frequency edge of the frequency band. The reference voltage signal can correspond any of a lowest or a highest value of the output of the charge to voltage conversion circuit. In an embodiment, the differential amplifier circuit amplifies the difference between its inverting and non-inverting inputs. The inverting input of the differential amplifier circuit 108 can be V_F voltage, and the non-inverting input can be the output from the charge to voltage converting circuit 106. The V_F can be a fixed voltage which can be decided based on the analysis of the charge to voltage converting circuit 106. This V_F voltage can be compared with the output of the charge to voltage converting circuit 106 to generate a zero-voltage difference at minimum output voltage, V_F. At the maximum voltage the difference voltage can go to its highest level. This difference voltage can be amplified by the gain factor of differential amplifier.
[0046] As illustrated in FIG. 2, the proposed circuit can be implemented in RF circuit after the sampling of input signal. The output voltage of the proposed circuit can be interfaced by digital or analog means to control the single pole ‘N’ throw (SPNT) at an input and ‘N’ poles single throw (NPST) at an output of switched RF systems bank. The same system at end of conversion can turn the main RF path ON by controlling supply of ICs in the Main RF path. An interface circuit in the FIG. 2 can include any of a window comparator (FIG. 3A) or an analog to digital converter (FIG. 3B).
[0047] Moreover, in interpreting the specification, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refer to at least one of something selected from the group consisting of A, B, C ….and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.
[0048] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions, or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION
[0049] The proposed invention provides a circuit for sensing a frequency of an input signal of RF band, which allow frequency sensing of the high frequency signals.
[0050] The proposed invention provides a circuit for sensing a frequency of an input signal of RF band, which allow auto switching of the RF networks based in the sensed frequency.
[0051] The proposed invention provides a circuit for sensing a frequency of an input signal of RF band, which allow designer to design switched RF networks with subsystems such as narrowband filters, matching networks, driver, amplifier or attenuators to meet required criterion of the application. 
, Claims:1. A circuit for sensing a frequency of an input signal, in a frequency band, of an RF subsystem, the circuit comprises:
a pre-scaler circuit configured to receive the input signal, and the pre-scaler circuit is configured to divide the frequency of the input signal into a plurality of samples;
an error detection circuit configured to receive an output of the pre-scaler circuit, wherein the error detection circuit is configured to generate an error signal based on comparison between a reference frequency and each of the plurality of samples;
a charge to voltage converting circuit configured to receive the error signal and outputs a voltage signal proportional to the error signal; and
a differential amplifier circuit having a first input coupled to an output of the charge to voltage conversion circuit and a second input configured to receive a reference voltage signal, and the differential amplifier is configured to output a voltage corresponding to a frequency within the frequency band, wherein power supply voltages of the differential amplifier are corresponding to a lower frequency edge and an upper frequency edge of the frequency band.
2. The circuit as claimed in claim 1, wherein the pre-scaler circuit comprises a frequency divider.
3. The circuit as claimed in claim 1, wherein the error detection circuit comprises any or combination of a phase frequency detector, and a charge pump.
4. The circuit as claimed in claim 1, wherein the charge to voltage converting circuit comprises a voltage amplifier.
5. The circuit as claimed in claim 1, wherein the reference frequency is different that a pre-scaled frequency of the plurality of samples for avoiding any occurrence of blank pulses at the output of error detection circuit.
6. The circuit as claimed in claim 1, wherein the reference voltage signal corresponds any of a lowest or a highest value of the output of the charge to voltage conversion circuit.
7. The circuit as claimed in claim 1, wherein a gain of differential amplifier circuit corresponds to dynamic range V1 to V2 (where V1 and V2 are the minimum and maximum output voltage levels).
8. The circuit as claimed in claim 1, wherein the frequency of the input signal is in a range F1 to F2 where F2 is greater than F1.