JPH04269041A - Receiver - Google Patents

Abstract

PURPOSE:To form a receiver able to trace a fast change in a center frequency by converting a multi-carrier signal whose center frequency differs into a base band signal whose center frequency is zero through the use of a sampling clock signal in response to the center frequency of each channel. CONSTITUTION:An RF modulation signal is multiplied with an oscillating frequency of a frequency synthesizer and the result is converted into a 1st IF frequency. On the other hand, since a disturbing wave signal of an adjacent channel is distorted and incorporated into a reception band in the case of amplification in an AGC amplifier 410 in a 2nd IF frequency, the adjacent channel is sufficiently attenuated by a filter 409 in advance. A modulation signal amplified by a limiter amplifier is subjected to orthogonal detection by an orthogonal modulator while keeping a frequency offset. Then output I, Q channel signals are converted into base band signals whose center frequency is zero by using a sampling clock signal in response to the offset frequency at frequency conversion filters 415, 416.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver used for frequency hopping transmission in digital communications.

0002

2. Description of the Related Art When performing high-speed transmission of several hundred kbps or more in land mobile communications, propagation characteristics deteriorate due to frequency selective fading due to multiple wave propagation. Errors that are difficult to reduce (floor errors) caused by this frequency selective fading are dominated by burst errors, and error correction codes such as Reed-Solomon codes, which are burst error correction codes, are used to correct floor errors. It will be done. If the fading frequency is low and the level of the entire burst is reduced, errors cannot be corrected even if error correction is performed. Therefore, in this case, a method is used in which frequency diversity such as frequency hopping is performed to hop the center frequency in bit units to randomize errors. In other words, frequency hopping involves hopping to a different center frequency for each bit or frame, and when applied to mobile communications, it randomizes the frequency diversity effect and burst errors under frequency selective fading and facilitates error correction. It is.

Conventional FH receivers have a configuration in which channels are specified using a frequency synthesizer, and it is necessary to switch between stable frequencies at high speed.

FIG. 1 shows the configuration of an FH receiver using a conventional frequency synthesizer. The method using a frequency synthesizer requires a frequency synthesizer that can switch between stable frequencies at high speed. The configuration of a frequency synthesizer can be broadly divided into 1. Direct synthesis method, 2. It can be classified as an indirect synthesis method. The direct synthesis method is a method in which harmonics are generated from a stable signal and a desired frequency component is obtained by multiplication between the harmonics or multiplication between the harmonics and a frequency-divided wave. This method allows high-speed switching of frequencies in a few μs or less, but it increases the circuit scale due to the large number of mixer and multiplier circuit components, and also causes a considerable increase in spurious signals, making it difficult to synthesize stable signals. , it becomes extremely difficult.

The indirect synthesis method is a method in which the output frequency is synchronized with the reference frequency using a frequency divider and a PLL, and as compared with the direct synthesis method, there is less spurious and the circuit is smaller. However, it is impossible to make the frequency switching time shorter than the time constant of the LPF in the loop, and is generally several tens of milliseconds to several seconds, and if an attempt is made to make the switching time faster, the frequency stability of the VCO output signal deteriorates. For this reason, methods for improving the PLL pull-in characteristics include (1) lowering the time constant or increasing the loop gain only during pull-in; (2)
(3) A method of effectively switching the loop gain by switching the phase comparison frequency; (3) A method of improving the loop response characteristics by using a notch filter instead of an LPF to remove the second harmonic component; (4) When switching the frequency division ratio, there are methods such as superimposing a DC voltage corresponding to the desired frequency on the VCO input using a D/A converter, bringing the VCO output frequency as close to the desired frequency as possible, and drawing in only the difference frequency. Although it is being considered, it is insufficient to achieve high-speed switching and frequency stability.

The rise time of frequency synthesizers used in mobile and portable devices of current car telephone systems is about 1 ms, and when frequency hopping is performed bit by bit, there are restrictions on the data transmission rate. Since one frequency synthesizer cannot perform high-speed channel switching, two frequency synthesizers are prepared as shown in B in Figure 2. For example, if the center frequency hops for each bit, the channel can be specified using odd and even bits. There is also a method of using separate frequency synthesizers, but this increases the circuit scale and is not suitable for mobile devices and portable devices.

[0007] Therefore, a receiver is required that can demodulate signals having different center frequencies at high speed.

[0008]

[Problems to be Solved by the Invention] In the method of frequency converting RF modulated signals with different center frequencies into IF signals of the same frequency using a frequency synthesizer as in the conventional FH receiver, the frequency switching time is the time constant of the loop filter. It is difficult to switch channels on a bit-by-bit basis for high-speed signals.

[0009] The present invention is a baseband signal processing circuit,
The purpose of this invention is to realize an FH receiver that is capable of high-speed channel switching and is suitable for circuit miniaturization.

0010

[Means for Solving the Problems] FIG. 1 is a block diagram showing the basic configuration of a receiver according to the present invention.

[0011] The present invention provides an IF for attenuating adjacent channel signals for each channel signal having a different center frequency.
A filter 105, a limiter amplifier or AGC amplifier 106 that amplifies the IF signal to a required level, a mixer 107, a hybrid 108, a 90-degree phase shifter 109, and a local oscillator 110 that amplify the IF signal with a different center frequency.
a frequency conversion filter (including a sample value system filter that removes harmonic components after quadrature detection and samples at the center frequency of each channel); L
PF) 111, 112, A/D converters 113, 114 that convert the baseband signal output from the frequency conversion filter into digital values, and a quasi-synchronous detector, which includes a clock synchronization circuit, a carrier frequency error extraction circuit, and a carrier frequency error. The guarantee circuit and delay detector include a digital signal processing demodulation section 115 including a circuit for detecting a phase difference with data one time slot before, a clock synchronization circuit, and the like.

[0012] The present invention provides a method in which RF signals with different center frequencies are used in advance.
Frequency conversion of the signal to the IF frequency with the center frequency offset, band limiting with the IF body, amplification to the required level, and after quadrature detection, use the folded signal to the baseband band (center frequency zero) by sampling. It is characterized by converting a signal with a frequency offset at high speed into a same channel signal (zero frequency), and demodulating it by digital processing after A/D conversion.

[0013]

[Operation] The RF modulated signal expressed as cos [φi + (ωc + Δωn) t] is frequency-converted to the IF band with the center frequency offset, and after removing unnecessary signals of adjacent channels with the IF filter, it is passed through the limiter amplifier or , is amplified to about -10 dBm by the AGC amplifier. The amplified IF signal is orthogonally detected by a quadrature detector. Quadrature detector I channel output cos [φi+Δωnt]
, the Q channel output sin[φi+Δωnt] has the harmonic components removed, and then the center frequency Δfn(
Δfn=Δωn/2π). After sampling, the fundamental wave and harmonic components are removed using an analog low-pass filter (LPF) that extracts only the baseband folded signal. The baseband signal is converted into a digital signal by an A/D converter, and demodulated by arithmetic processing in a digital processing demodulation section.

FIG. 3 is a diagram illustrating the principle of the FH receiver of the present invention in the frequency domain.

After removing harmonic components from the frequency-offset analog signal after orthogonal detection using an LPF,
There is also a method of sampling with a digital filter after A/D conversion and processing with a digital LPF, but in this case, the highest frequency of the signal becomes higher by the offset of the center frequency, and therefore the sampling frequency of the A/D converter also increases. Since it is expensive, it is disadvantageous in terms of power consumption.

[0016]

Embodiment FIG. 4 shows an embodiment of the FH receiver of the present invention in a double conversion type receiver. 404 in the diagram
is a frequency synthesizer, 405 is a BPF, 406 is an amplifier, 407 is a mixer, 408 is an oscillator, 409 is a second I
F filter ladder, 410 is limiter amplifier or AG
C amplifier, 415, 416 are frequency conversion filters, 41
7,418 is an A/D converter, and 419 is a digital signal processing demodulation section.

The RF modulated signal is multiplied by the oscillation frequency of the frequency synthesizer and frequency converted to the first IF frequency. Since the first IFBPF 405 is a filter for removing image signals of the second IF frequency, a wide band is set so that the entire hopping frequency band of a certain channel is used as a pass band. The limiter amplifier or AGC amplifier 410 at the second IF frequency requires a dynamic range of 70 dB or more, and during amplification, the interference wave signal of the adjacent channel is distorted and falls within the reception band.
It is necessary to sufficiently attenuate the adjacent channel signal using the second IF filter 409 in advance. 2nd IF with different center frequency
For example, if the filter has a frequency of about 10 MHz, it is composed of a ceramic filter, and if the center frequency can be lowered to several MHz, it is possible to use a monolithic IC. The modulated signal amplified by the limiter amplifier is orthogonally detected by a quadrature modulator while maintaining the frequency offset. The orthogonally detected I and Q channel signals are passed through a frequency conversion filter 4.
15, 416, the I and Q channel signals are converted into baseband signals using sampling clock signals according to the offset frequency, and further converted into signals with a center frequency of zero. Band delay detection is performed. Delay detection is performed by performing the following calculation using multiplication and addition operations. cos(φn-φn-1)=cos(φn)co
s(φn-1)+sin(φn)sin(φn-1)
(1) sin(φn-
φn-1)=sin(φn)cos(φn-1)-c
os(φn)sin(φn-1)
(2) Quasi-synchronous detection is performed by detecting a carrier frequency error from demodulated data and compensating it to the demodulated data.

FIG. 5 shows an embodiment of the frequency conversion filter and the frequency characteristics of each block. The first stage is a filter that removes harmonic components after quadrature detection, and OTA (Oper
ational Transconductance A
It consists of a high-precision analog filter such as a mplifier filter. An example of a second-order OTA filter is shown in FIG. The OTA filter is a high-precision analog filter that is composed of an OTA amplifier and a capacitor and can be easily fabricated into a monolithic IC. The frequency characteristics of the second and third stages as a whole have a characteristic of removing signal components before frequency conversion. Second
The stage is of low order compared to the third stage, and the second stage is SCF (S
witched Capacitor Filter)
Consists of. FIG. 6 shows an example of a first-order integrator that constitutes the SCF. The SCF is a high-precision sample value filter consisting of an amplifier, a capacitor, and an analog switch. The third stage is O
Consists of a TA filter. The above-mentioned OTA filter and SCF are filters whose frequency characteristics can be varied by changing the external clock frequency. Current mobile devices internally include a 12.8 MHz high stability (3 ppm) voltage compensated crystal filter (TCXO). For example, by changing the frequency division ratio of this TCXO output signal using a frequency divider, it can be used as a control signal for a frequency conversion filter.

[0019]

As explained above, according to the present invention, multi-carrier signals with different center frequencies are processed by a baseband circuit using folded signals of sampled value filters according to the center frequency of each channel. Since it is converted into a baseband signal with zero frequency, it is possible to configure a receiver that can follow rapid changes in the center frequency, unlike the conventional method using a frequency synthesizer.

[Brief explanation of the drawing]

[Fig. 1] Principle configuration diagram of the FH receiver of the present invention

[Figure 2] FH receiver configuration diagram using a conventional frequency synthesizer

FIG. 3 is an explanatory diagram of the operation of the FH receiver of the present invention in the frequency domain.

FIG. 4: Embodiment of the FH receiver of the present invention

[Figure 5] Example of frequency conversion filter of the present invention

FIG. 6 shows an example of a frequency conversion filter.

[Explanation of symbols]

101 RF modulation signal input terminal 102 Data output terminal 103 Mixer 104 Frequency synthesizer 105 IF filter 106 Limiter amplifier or AGC amplifier 107
Mixer 108 Hybrid 109 90 degree phase shifter 110 Local oscillator 111 Frequency conversion filter 112 Frequency conversion filter 113 A/D converter 114 A/D converter 115 Digital signal processing demodulator 201 RF modulation signal input terminal 202 Data output terminal 203 Bandpass filter (BPF) 204 Mixer 205 Frequency synthesizer 206 Bandpass filter (BPF) 207 AG
C or limiter 208 Demodulator 209 RF modulation signal input terminal 210 Data output terminal 211 Bandpass filter (BPF) 212 Mixer 213 Changeover switch 214 Frequency synthesizer 215 Frequency synthesizer 216 Bandpass filter (BPF) 217 AG
C or limiter 218 Demodulator 401 RF modulation signal input terminal 402 Data output terminal 403 Mixer 404 Frequency synthesizer 405 First IF filter 406 Amplifier 407 Mixer 408 Oscillator 409 Second IF filter 410 AGC or limiter 411 Mixer 412 Hybrid 413 90 degree phase shifter 414 Oscillator 415 Frequency conversion filter 416 Frequency conversion filter 417 A/D converter 418 A/D converter 419 Digital signal processing demodulator 420 Voltage compensated crystal oscillator 421 Frequency divider

Claims (1)

[Claims] Claim 1: In a receiver that uses a frequency synthesizer to perform frequency conversion on modulated RF signals with different center frequencies, the intermediate frequency (IF) signals with different center frequencies are band-limited. a plurality of band pass filters (BPF) with different center frequencies;
A limiter amplification stage or AGC amplifier that amplifies the band-limited signal by the PF, and a c
This modulated signal is expressed as os[φi+2π(fc+Δfn)t] (where φi is the modulation component, fc is the intermediate carrier frequency, and Δfn is the frequency between the center frequency of channel n and fc), and this modulated signal is transmitted from the local oscillator at the oscillation frequency fc. I channel signal c
os[φi+2πtΔfn] and Q channel signal sin[
φi+2πtΔfn], and a sample value that samples the orthogonally detected I-channel signal and Q-channel signal at a frequency Δfn, respectively, and converts them into a baseband signal using a folded signal with a center frequency of zero. A receiver comprising: a frequency conversion filter including a system filter.