JP2011114440A - Differential signal generation circuit and frequency conversion circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve an S/N ratio in a differential signal generation circuit. <P>SOLUTION: The differential signal generation circuit 31 includes: a source grounding circuit 311 for amplifying an inputted RF signal; a drain grounding circuit 312 for generating differential signals RF<SB>+</SB>and RF<SB>-</SB>of the amplified RF signal; and a capacity part 313 for adjusting a phase difference between the generated differential signals RF<SB>+</SB>and RF<SB>-</SB>. A first resistor R1 and a second resistor R2 in the drain grounding circuit 312 equalize the amplitude of the differential signals RF<SB>+</SB>and RF<SB>-</SB>, and the capacitor part 313 adjusts the phase difference between the differential signals RF<SB>+</SB>and RF<SB>-</SB>to be almost 180 degrees. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a differential signal generation circuit and a frequency conversion circuit including the differential signal generation circuit.

  A superheterodyne wireless communication apparatus uses a mixer that multiplies (synthesizes) a received signal by a local oscillation signal (local signal) generated inside the apparatus and converts the received signal into an intermediate frequency signal (IF signal). At this time, in order to increase the conversion efficiency, a mixer (for example, a Gilbert cell mixer) that inputs a differential signal as an input signal is used, and the received signal is amplified and converted into a differential signal at the front stage of the mixer. A differential amplifier circuit is provided. As this differential amplifier circuit, for example, as disclosed in Patent Document 1, a configuration using a differential transistor pair in which two transistors having the same characteristics are symmetrically connected is generally used.

JP 2007-208612 A

  By the way, when receiving a high-frequency signal of 1 GHz or higher such as a GPS signal, there is a problem of a decrease in S / N ratio due to noise generated by constituent elements (amplifying elements, load elements, etc.) of the differential amplifier circuit. Further, when a plurality of stages of differential amplifier circuits are connected in order to increase the degree of amplification, the degree of reduction in the S / N ratio increases as the number of circuit elements increases. The present invention has been made in view of the above circumstances, and an object thereof is to improve the S / N ratio in a differential signal generation circuit.

  A first form for solving the above problem is provided in a grounded source circuit to which a specified high-frequency signal of 1 GHz or more is input to a gate, and an output stage of the grounded source circuit, and a drain is provided via a first resistor. A power source line, a source grounded through a second resistor, a drain and a drain ground circuit that outputs a differential signal of the specified high-frequency signal from the source, and the first resistor and the second resistor The resistor is a differential signal generation circuit having a resistance value for equally adjusting the amplitudes of the output signals from the drain and the source of the grounded drain circuit.

  According to the first aspect, a differential including a source grounded circuit to which a specified high-frequency signal is input, and a drain grounded circuit that is provided at an output stage of the source grounded circuit and outputs a differential signal of the specified high-frequency signal. A signal generation circuit is configured. That is, the input specified high-frequency signal is amplified by the source ground circuit, and the differential signal of the amplified specified high-frequency signal is generated by the drain ground circuit. As a result, since only one transistor of the common source circuit is required as an amplifying element, the number of amplifying elements can be reduced as compared with a conventional differential amplifying circuit using a differential transistor pair. A differential signal generation circuit that prevents a decrease in the N ratio can be realized.

  Further, the amplitudes of the output signals from the drain and the source are adjusted equally by the first resistor and the second resistor in the common drain circuit. Thereby, a differential signal having substantially the same amplitude is generated.

  A second form is a differential signal generation circuit according to the first form, wherein the phase difference of the output signals from the drain and the source is between the source of the grounded drain circuit and the output terminal of the differential signal. A differential signal generation circuit provided with a capacitor for adjusting the angle to 180 degrees may be configured.

  According to the second embodiment, the phase difference between the output signals from the drain and the source is adjusted to 180 degrees by the capacitance provided between the source of the common drain circuit and the output terminal of the differential signal. As a result, a differential signal whose phase difference is adjusted to approximately 180 degrees is generated.

  Further, as a third mode, a frequency conversion circuit that multiplies a received signal of a specified high-frequency signal of 1 GHz or more by a local oscillation signal and extracts a signal having a difference frequency between the harmonic of the local oscillation signal and the frequency of the specified high-frequency signal. A differential signal generation circuit of the first or second form for inputting the reception signal, and a mixer unit for multiplying each of the differential signals output from the differential signal generation circuit by the local oscillation signal; A frequency conversion circuit including a filter unit that extracts the signal component of the difference frequency from the output signal of the mixer unit may be configured.

The block block diagram of a GPS receiver. The block block diagram of a frequency conversion part. The circuit block diagram of a differential signal generation circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following, the case where the present invention is applied to a GPS receiver that receives a GPS signal transmitted from a GPS (Global Positioning System) satellite, which is a kind of positioning satellite, will be described. However, the embodiment is not limited to this.

[Constitution]
FIG. 1 is a block configuration diagram of a GPS receiver 1 according to the present embodiment. As shown in FIG. 1, the GPS receiver 1 includes a GPS antenna 10, an RF (Radio Frequency) receiving circuit unit 20, and a baseband unit 40.

  The GPS antenna 10 receives an RF signal including a GPS satellite signal transmitted from a GPS satellite that is a kind of positioning satellite. The GPS satellite signal is a 1.57542 [GHz] communication signal directly modulated by a spread spectrum system with a PRN (Pseudo Random Noise) code, which is a kind of spreading code different for each GPS satellite. The PRN code is a pseudo random noise code having a repetition period of 1 ms with a code length of 1023 chips as one frame.

  The RF receiving circuit unit 20 includes a SAW (Surface Acoustic Wave) filter 21, an LNA (Low Noise Amplifier) 22, a frequency conversion unit 30, an amplification unit 23, and an ADC (Analog to Digital Converter) 24.

  The SAW filter 21 is a band-pass filter, and allows a signal in a predetermined band to pass through the RF signal received by the GPS antenna 10 and blocks out-of-band frequency components. The LNA 22 is a low noise amplifier and amplifies the RF signal output from the SAW filter 21.

  The frequency conversion unit 30 multiplies the RF signal output from the LNA 22 by a predetermined local oscillation signal Lo, and converts the RF signal into an intermediate frequency signal (IF signal). The amplification unit 23 amplifies the IF signal output from the frequency conversion unit 30. The ADC 24 converts the IF signal that is an analog signal output from the amplifying unit 23 into a digital signal.

  The baseband unit 40 performs correlation processing on the IF signal output from the RF receiving circuit unit 20 to capture and extract GPS satellite signals, decodes the data to extract navigation messages and time information, and calculates pseudo distances. And positioning calculation.

  FIG. 2 is a block configuration diagram of the frequency conversion unit 30. As shown in FIG. 2, the frequency conversion unit 30 includes a differential signal generation circuit 31, a local oscillation signal generation unit 32, a differential conversion circuit 33, a mixer 34, and an LPF 35.

The differential signal generation circuit 31 amplifies the RF signal input from the LNA 22 and converts it into differential signals RF ₊ and RF ₋ .

The local oscillation signal generation unit 32 includes an oscillator such as a VCO (Voltage Controlled Oscillator) and generates a local oscillation signal (local signal) Lo having a frequency F _Lo . The differential conversion circuit 33 converts the local oscillation signal Lo from the local oscillation signal generation unit 32 into differential signals Lo ₊ and Lo ₋ .

The mixer 34 is realized by a Gilbert cell mixer composed of a plurality of MOS transistors. An RF signal is input from the differential signal generation circuit 31 to the mixer 34 as differential signals RF ₊ and RF ₋ , and a local oscillation signal Lo is input from the differential conversion circuit 33 to the differential signals Lo ₊ and Lo. _- is input as the signal MIX obtained by multiplying the RF signal and the local oscillation signal Lo, the signal of the differential type _MIX +, MIX _- output as.

The LPF 35 passes a low-band signal including a difference frequency between the RF signal and the local oscillation signal Lo with respect to the signal output from the mixer 34, and blocks out-of-band frequency components. The LPF 35 extracts desired IF signals IF ₊ and IF ₋ from the output signal of the mixer 34. Since the differential signals IF ₊ and IF ₋ are used, either one of the signals may be used as an IF signal in the subsequent circuit, or the differential voltage between the differential signals IF ₊ and IF ₋ may be used. May be used as an IF signal.

  FIG. 3 is a circuit configuration diagram of the differential signal generation circuit 31. As shown in FIG. 3, the differential signal generation circuit 31 includes a source ground circuit 311, a drain ground circuit 312, and a capacitor unit 313.

The source ground circuit 311 is a circuit in which the MOS transistor TR1 is grounded, and amplifies the input RF signal. The RF signal from the LNA 22 is applied to the gate terminal G of the MOS transistor TR1 via the capacitor C1 for cutting off the DC component, the source terminal S is grounded, and the drain terminal D is connected to the power supply line Vdd via the load resistor _RL. It is connected to the. The output Vd1 from the drain terminal D of the MOS transistor Tr1 becomes the output signal of the source ground circuit 311.

The drain ground circuit 312 is a circuit (source follower) in which the MOS transistor TR2 is grounded to the drain, and is provided at the output stage of the source ground circuit 311. The differential signal RF ₊ , the RF signal amplified by the source ground circuit 311 is provided. RF ₋ is generated.

The output signal of the previous source installation circuit 311 is applied to the gate terminal G of the MOS transistor TR2 via the DC component blocking capacitor C2, and the drain terminal D is connected to the power supply line Vdd via the first resistor R1. The source terminal S is connected and grounded (GND) via the second resistor R2. The outputs from the drain terminal D and source terminal S of the MOS transistor TR2 Vd2, Vs becomes the output signal of the common source circuit 311, the drain terminal D is the differential output terminal RF _- is connected to the source terminal S is capacity It is connected to the differential output terminal RF ₊ via the part 313.

Here, the resistance values of the first resistor R1 and the second resistor R2 in the common drain circuit 312 are determined so that the amplitudes of the differential signals RF ₊ and RF ₋ are equal.

The capacitor unit 313 is provided between the source terminal S of the MOS transistor TR2 and the differential output terminal RF _+, and is a capacitor element for adjusting the phase of the output signal Vs from the source terminal S of the MOS transistor TR2. Become. That is, the output Vd2 from the drain terminal D of the MOS transistor TR2 and the output Vs from the source terminal S are signals that are almost 180 degrees out of phase, but are completely affected by the parasitic resistance and parasitic capacitance of the MOS transistor Tr2. However, there is a slight error. The capacitance unit 313 adjusts the error of the phase difference between the outputs Vd2 and Vs, and the capacitance value C is determined so that the phase difference between the differential signals RF ₊ and RF ₋ is completely 180 degrees.

  Note that the capacitor 313 can be composed of discrete elements, but it is a capacitor for adjusting the phase of a high-frequency signal of 1 GHz or more, and thus a minute capacitor is sufficient. Therefore, in the present embodiment, as an example, a junction capacitor or a substrate parasitic capacitance is used as a capacitor element by short-circuiting a resistor element formed of a well resistor.

[Action / Effect]
As described above, in the GPS receiver 1 according to the present embodiment, the differential signal generation circuit 31 includes the source grounding circuit 311 that amplifies the input RF signal, and the differential signals RF ₊ and RF _{− of the} amplified RF signal. The drain grounding circuit 312 for generating the signal and the capacitor unit 313 for adjusting the phase difference between the generated differential signals RF ₊ and RF ₋ are configured. That is, since only the MOS transistor TR1 of the source grounded circuit 311 is required as an amplifying element, the number of amplifying elements is reduced and the S / N ratio is reduced as compared with a conventional differential amplifying circuit using a differential transistor pair. The differential signal generation circuit 31 is improved. The first and second resistors R1 and R2 in the grounded drain circuit 312 have the same amplitude of the differential signals RF ₊ and RF ₋ , and the capacitance unit 313 allows the differential signals RF ₊ and RF ₋ to be The phase difference is adjusted to be approximately 180 degrees.

[Modification]
It should be noted that embodiments to which the present invention can be applied are not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention.

(A) Capacitor 313
For example, the capacitor 313 may be provided on the drain terminal D side instead of the source terminal S side of the MOS transistor TR2 of the drain ground circuit 312 or may be provided on both the source terminal S and the drain terminal D side. good.

(B) Mixer 34
In the above-described embodiment, the mixer 34 is a Gilbird cell mixer. However, any mixer may be used as long as an input signal is input in a differential format, such as a double balance type mixer.

(C) Receiving Device In the above-described embodiment, the GPS receiving device 1 that receives GPS signals is used. However, the receiving device that receives satellite signals in other satellite positioning systems such as GLONASS (GLObal Navigation Satellite System) is also used. The same applies.

DESCRIPTION OF SYMBOLS 1 GPS receiver, 10 GPS antenna, 20 RF receiving circuit part, 21 SAW filter, 22 LNA, 23 Amplifying part, 24 ADC, 30 Frequency conversion part, 31 Differential signal generation circuit, 32 Local oscillation signal generation part, 33 Difference Dynamic conversion circuit, 34 mixer, 35 LPF, 40 baseband section, 311 source ground circuit, 312 drain ground circuit, 313 capacitance section, TR1 MOS transistor, Tr2 MOS transistor

Claims (3)

A grounded source circuit in which a specified high-frequency signal of 1 GHz or more is input to the gate;
Provided at the output stage of the grounded source circuit, the drain is connected to the power supply line through the first resistor, the source is grounded through the second resistor, and the differential of the specified high-frequency signal from the drain and the source A grounded drain circuit for outputting a signal;
With
The first resistor and the second resistor are resistance values for adjusting the amplitude of the output signal from each of the drain and the source of the common drain circuit,
Differential signal generation circuit. A capacitor for adjusting the phase difference of the output signals from the drain and the source to 180 degrees is provided between the source of the grounded drain circuit and the output terminal of the differential signal.
The differential signal generation circuit according to claim 1. A frequency conversion circuit for multiplying a reception signal of a specified high frequency signal of 1 GHz or more by a local oscillation signal and extracting a signal having a difference frequency between a harmonic of the local oscillation signal and the frequency of the specified high frequency signal,
The differential signal generation circuit according to claim 1 or 2, wherein the reception signal is input;
A mixer unit that multiplies each of the differential signals output from the differential signal generation circuit by the local oscillation signal;
A filter unit for extracting the signal component of the difference frequency from the output signal of the mixer unit;
A frequency conversion circuit comprising:

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