KR20050078494A - Frequency conversion in a receiver - Google Patents

Abstract

A frequency conversion method of a receiver comprises receiving a signal having a radio frequency and carrying information on a plurality of channels, selecting one of the channels, and a first variable frequency determined by the channel selected from the radio frequency; And converting the signal from the first variable frequency to a desired frequency.

Description

Frequency conversion of the receiver {FREQUENCY CONVERSION IN A RECEIVER}

TECHNICAL FIELD The present invention relates to frequency conversion, and in particular, to double or triple frequency conversion of RF signals of a TV tuner.

Broadband tuners are used in a variety of consumer and commercial systems, such as TVs, VCRs, and more complex devices, including cable modems and cable set-top boxes. Over 3 million broadband tuners are produced each year.

More and more services are provided through broadcast TV and cable operators, resulting in a rapidly developing and concentrated market. The vision of incorporating DVD, VCR, Personal Video Recording and Internet functions into TV sets, set-top boxes or even personal computers is an important feature of future media centers.

Acting as the RF front-end of the wideband signal, the tuner is responsible for receiving all available channels, selecting the desired channel and filtering out other channels. Tuners operating over the 40 to 900 MHz frequency range have different performance requirements than traditional TV tuners. Smaller shape factors, lower power consumption, higher reliability and ease of manufacture are new concerns in recent tuner applications.

For a TV tuner, the frequency conversion structure is essential to the tuner design. In US Pat. No. 5,737,035, Robert Rudolf Rotzoll et al. Describe a highly integrated dual frequency converted television tuner on a single microcircuit, as shown in FIG. The RF signal enters the TV tuner 1100 from the antenna 1402 (or a cable not shown) and passes through an RF low-pass filter (RFLPF) 1404 with an incomingcoming band of 900 Limited to less than MHz. The filtered RF signal is amplified up to 20 dB by a gain-controlled low-noise transconductance amplifier (LNTA) 1406.

The output of the first local oscillator (LO1) 1450 operating between 1200 and 2100 MHz is mixed with the RF signal in the first mixer MIX1 1408 to generate a first IF video carrier frequency of 1200 MHz. This solution minimizes distortion due to mixer image and harmonic mixing. The first IF is filtered as is by the bandwidth limitation of the first mixer 408 to minimize harmonic effects.

The first IF signal of 1200 Hz is mixed with a fixed 1180 MHz reference output of a second local oscillator (LO2) 1412 in a second mixer (MIX2) 1410, which is an image-rejection mixer, 20 MHz. A second IF is generated on the visual carrier. Since the RF input signal is lower in frequency than the reference LO, the mixing of the two signals results in down conversion of the RF input.

However, in the above-described TV tuner, out-of-band channels must be removed by an external RF Surface Acoustic Wave (SAW) filter, which requires a highly linear SAW driver that requires large power consumption on the tuner chip. Shall be. In addition, a phase lock loop (PLL) circuit that generates an oscillation signal for the first mixer operates at a high frequency, resulting in a spurious output of the first mixer.

An object of the present invention is to provide a TV tuner with a low number of components, low power consumption and high signal-to-noise ratio.

The present invention comprises the steps of receiving a signal having a radio frequency and carrying information of a plurality of channels, selecting one of the channels, and converting the signal from a radio frequency to a first variable frequency determined by the selected channel And converting the signal from the first frequency to the second frequency.

The present invention provides an antenna for receiving an RF signal carrying information of a plurality of channels, a first local oscillator for generating a first oscillation signal having a first variable frequency determined by a selected channel among the channels, and the RF signal. A first mixer that generates an intermediate signal by mixing with the first oscillating signal, a second local oscillator that generates a second oscillating signal having a second frequency, and a baseband by mixing the intermediate signal with the second oscillating signal And a second mixer for generating a signal, wherein the frequency of the intermediate signal is variable and determined by the selected channel.

The present invention provides an antenna for receiving an RF signal carrying information on a plurality of channels, a first local oscillator for generating a first oscillation signal having a first variable frequency determined by a selected channel among the channels, and the RF signal. Is mixed with the first oscillation signal to generate a first intermediate signal, a second local oscillator to generate a second oscillation signal having a second frequency, and the first intermediate signal to the second oscillation signal. A second mixer for generating a second intermediate signal by mixing with a third local oscillator for generating a third oscillating signal having a third frequency, and a baseband signal by mixing the second intermediate signal with the third oscillating signal And a third mixer for generating a second mixer, wherein the frequency of the first intermediate signal is variable and is selected by the selected channel.

The invention will be more fully understood from the following detailed description and drawings.

2 is a diagram showing a TV tuner according to an embodiment of the present invention. The TV tuner (receiver) includes an antenna 21 for receiving an RF signal carrying information of all TV channels, a low noise amplifier 22 connected to the antenna for amplifying the RF signal, and a first frequency FO1. A first local oscillator 23 for generating a first oscillation signal OS1 having a first mixer 24 for generating an intermediate signal IS by mixing an amplified RF signal with a first oscillation signal OS1; The second local oscillator 25 generating the second oscillation signal OS2 having the second frequency FO2 and the intermediate signal IS are mixed with the second oscillation signal OS2 to form a baseband signal ( A second mixer 26 generating a BS) and a SAW driver 27 connected to an output of the second mixer 26 to drive an external SAW filter (not shown).

The first local oscillator 23 and the first mixer 24 form a first frequency conversion stage for converting an RF signal from a radio frequency to a variable intermediate frequency IF determined by a selected TV channel. The frequency IF is determined to minimize noise and spurious signals that are higher than the radio frequency (upconversion) and are combined into a selected channel from another channel. The value of the frequency IF varies from channel to channel. The second local oscillator 25 and the second mixer 26 form a second frequency conversion stage for converting the signal from the frequency IF to the baseband frequency BF which is fixed for all channels (down conversion). The mixers 24 and 26 are image stop mixers that block in-band noise from image frequencies. Out-of-band signals are blocked by LC tanks (not shown) in the mixers 24 and 26.

3 is a diagram showing the oscillator 23. The oscillator includes a first frequency divider 231 for dividing the frequency FR of the reference signal RS by a divisor N and a first terminal connected to an output terminal of the first frequency divider 231. A loop filter having a phase frequency detector 232 having an input terminal, a charge pump 233 having an input terminal connected to an output terminal of the phase frequency detector 232, and an input terminal connected to an output terminal of the charge pump 233 ( A voltage controlled oscillator 235 having an input terminal connected to an output terminal of the loop filter 234, and a frequency of a signal output from the voltage controlled oscillator 235 by a divisor P and dividing the frequency of the first oscillation signal OS1. Frequency multiplier having a second frequency divider 236 for outputting a multiplier M and a multiplier M multiplied by the first oscillation signal OS1 and connected to a second input terminal of the phase frequency detector 232. 237). The divisor N and P and the multiplier M are determined by the selected channel. The frequency FO1 of the first oscillation signal OS1 is derived by the following equation.

FO1 = FR * M / (P * N)

4 is a diagram showing a TV tuner according to another embodiment of the present invention. The TV tuner applies triple frequency conversion rather than dual frequency conversion (shown in FIG. 2) to the RF signal. The TV tuner includes an antenna 41 for receiving RF signals carrying information from all TV channels, a low noise amplifier 42 connected to the antenna 41 to amplify the RF signal, and a first frequency FO1. A first local oscillator 43 for generating a first oscillation signal OS1 having a C1 and A mixer 44, a second local oscillator 45 for generating a second oscillation signal OS2 having a second frequency FO2, and the first intermediate signal IS1 to the second oscillation signal OS2. And a second mixer 46 for generating a second intermediate signal IS2, a third local oscillator 47 for generating a third oscillation signal OS3 having a third frequency FO3, and a second A third mixer 48 for mixing the intermediate signal IS2 with the third oscillation signal OS3 to generate a baseband signal BS, and an external SAW filter connected to an output terminal of the third mixer 48; SAW driver 49 for driving (not shown).

The first local oscillator 43 and the first mixer 44 form a first frequency conversion stage for converting an RF signal from a radio frequency to a variable intermediate frequency IF1 determined by the selected TV channel. The variable intermediate frequency IF1 is higher than the radio frequency (upconversion) and is determined to minimize noise and spurious signals that are coupled from the other channel into the selected channel. The value of the frequency IF1 varies from channel to channel. The second local oscillator 45 and the second mixer 46 convert the signal from the variable intermediate frequency IF1 to the second intermediate frequency IF2 which is fixed for all channels (down conversion). Form a stage. The third local oscillator 47 and the third mixer 48 form a third frequency conversion stage for converting the signal from the second intermediate frequency IF2 to the baseband frequency (down conversion). The mixers 44, 46, and 48 are image stop mixers that block in-band noise from image frequencies. Out-of-band signals are blocked by LC tanks (not shown) in the mixers 44, 46, 48.

Each oscillator 43, 45 is as shown in FIG. When the user selects a predetermined channel, the divisors N and P of each oscillator 43, 45 and the multiplier M are determined simultaneously.

Note that the triple frequency conversion tuner shown in FIG. 4 achieves wide-to-narrow band conversion and down conversion with two mixers 46 and 48, while FIG. The dual frequency conversion tuner shown achieves the same result with one mixer 26.

In conclusion, the present invention provides a TV tuner with fewer components, lower power consumption and high signal-to-noise ratio. In particular, compared to the TV tuner disclosed in US Pat. No. 5,737,035, the TV tuner of the present invention does not require an RF SAW filter to pre-process the signal sent to the TV tuner, requiring a highly linear SAW driver. Therefore, there is an advantage that the power consumption is reduced.

The foregoing descriptions of the preferred embodiments of the present invention have been presented for purposes of illustration and description. Obvious modifications and variations are possible in light of the above teachings. The above embodiments have been selected and described in order to best illustrate the principles of the invention and its practical application, and thus those skilled in the art can use the invention in various embodiments with various modifications to suit the particular intended use. All such modifications and variations fall within the scope of the present invention as determined by the appended claims when they are interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.

1 is a diagram showing a conventional TV tuner.

2 is a diagram showing a TV tuner according to an embodiment of the present invention.

3 is a diagram showing an oscillator of a TV tuner according to an embodiment of the present invention.

4 is a diagram showing a TV tuner according to another embodiment of the present invention.

Explanation of symbols for the main parts of the drawings

21, 41: antenna 22, 42: low noise amplifier

23, 43: first local oscillator 24, 44: first mixer

25, 45: second local oscillator 26, 46: second mixer

27, 49: SAW driver 47: third local oscillator

48: third mixer 231: first frequency unit

232: phase frequency detector 233: charge pump

234 loop filter 235 voltage controlled oscillator

236: second frequency divider 237: frequency multiplier

Claims (26)

Receiving a signal having a radio frequency and carrying a plurality of channels of information; Selecting one of the channels; Converting the signal from a radio frequency to a first variable frequency determined by the selected channel; Converting the signal from a first frequency to a second frequency Receiver frequency conversion method comprising a. 2. The method of claim 1, wherein the first frequency is determined to minimize noise coupled from another channel into the selected channel. The method of claim 1, wherein the first frequency is higher than the radio frequency. 2. The method of claim 1 wherein the second frequency is fixed for all channels. 2. The method of claim 1, wherein said second frequency is a baseband frequency. The method of claim 1, Converting the signal from a second frequency to a third frequency Frequency conversion method further comprises. 7. The method of claim 6, wherein the first frequency is determined to minimize noise coupled from another channel into the selected channel. 7. The method of claim 6 wherein the first frequency is higher than a radio frequency. 7. The method of claim 6, wherein the second frequency is fixed for all channels. 7. The method of claim 6, wherein said second frequency is lower than said first frequency. 7. The method of claim 6, wherein the third frequency is fixed for all channels. 7. The method of claim 6 wherein the third frequency is a baseband frequency. An antenna for receiving an RF signal carrying information of a plurality of channels; A first local oscillator for generating a first oscillation signal having a first frequency; A first mixer for mixing the RF signal with the first oscillating signal to generate an intermediate signal; A second local oscillator for generating a second oscillation signal having a second frequency; A second mixer for mixing the intermediate signal with the second oscillating signal to generate a baseband signal Wherein the frequency of the intermediate signal is variable and determined by the selected channel. The receiver of claim 13, wherein the frequency of the intermediate signal is determined such that noise coupled from another channel into the selected channel is minimized. The method of claim 13, wherein the first oscillator A first frequency dividing unit dividing the frequency FR of the reference signal RS by a divisor N, A phase frequency detector having a first input coupled to an output of the first frequency divider; A charge pump having an input connected to an output of the phase frequency detector, A loop filter having an input connected to an output of the charge pump; A voltage controlled oscillator having an input connected to an output of the loop filter; A second frequency dividing unit dividing the frequency of the signal output from the voltage controlled oscillator by divisor P and outputting a first oscillation signal OS1; A frequency multiplier having an output coupled to the first oscillation signal multiplied by a multiplier M and coupled to a second input of the phase frequency detector Receiver comprising a. 16. The receiver of claim 15 wherein the divisors N and P and the multiplier M are determined by the selected channel. 14. The receiver of claim 13, further comprising a low noise amplifier connected between the antenna and the first mixer to amplify the RF signal. The receiver of claim 13, further comprising a SAW driver coupled to the output of the second mixer. The receiver of claim 13, wherein the first mixer and the second mixer are video jersey mixers. An antenna for receiving an RF signal carrying information on a plurality of channels; A first local oscillator for generating a first oscillation signal having a first frequency; A first mixer for mixing the RF signal with the first oscillation signal to generate a first intermediate signal; A second local oscillator for generating a second oscillation signal having a second frequency; A second mixer for mixing the first intermediate signal with the second oscillation signal to generate a second intermediate signal; A third local oscillator for generating a third oscillation signal having a third frequency; A third mixer for mixing the second intermediate signal with the third oscillation signal to generate a baseband signal Wherein the frequency of the first intermediate signal is variable and determined by the selected channel. 21. The receiver of claim 20 wherein the frequency of the first intermediate signal is determined to minimize noise coupled from another channel into the selected channel. The method of claim 20, wherein each of the first oscillator and the second oscillator, A first frequency divider dividing the frequency (FR) of the reference signal by divisor N, A phase frequency detector having a first input coupled to an output of the first frequency divider; A charge pump having an input connected to an output of the phase frequency detector, A loop filter having an input connected to an output of the charge pump; A voltage controlled oscillator having an input connected to an output of the loop filter; A second frequency divider which divides the frequency of the signal output from the voltage controlled oscillator by divisor P and outputs the first oscillation signal; A frequency multiplier having an output coupled to the first oscillation signal multiplied by a multiplier M and coupled to a second input of the phase frequency detector Receiver comprising a. 23. The receiver of claim 22 wherein the divisors N and P and the multiplier M are determined by the selected channel. 21. The receiver of claim 20, further comprising a low noise amplifier coupled between the antenna and the first mixer to amplify the RF signal. 21. The receiver of claim 20 further comprising a SAW driver coupled to the output of the third mixer. 21. The receiver of claim 20 wherein the first mixer, the second mixer, and the third mixer are video jersey mixers.