Inexpensive receiver with integrated inductors

Abstract

Receiving device (300), comprising: a first amplifier (108) which has an input for receiving a radio frequency signal and which has an output; a first variable capacitor (502) having a first terminal connected to the output of the first amplifier and a second terminal connected to a first supply voltage terminal; and a transformer (504) comprising: a primary winding (506) with a first terminal connected to the first terminal of the first variable capacitor and a second terminal connected to a second supply voltage terminal, and a secondary winding (508) comprising a first terminal and a second terminal to output a filtered radio frequency difference signal, the secondary winding having a greater number of turns than the primary winding.

Description

AREA OF REVELATION

[0001] The present disclosure relates generally to receiver circuits and, more particularly, to receiver circuits that can be configured to receive ultra-high frequency and very high frequency broadcast signals. GENERAL STATE OF THE ART

[0002] Receiver circuits are used for both terrestrial and cable reception in televisions, digital video recorders, videocassette recorders, set-top boxes (e.g., cable and satellite tuners), frequency modulation (FM) radios, models, and other electronic devices. Some smartphones also use receiver circuits for television reception. Such receiver circuits generally include a tuner or tuning device that selects a narrowband signal from a wideband or broadband signal with multiple channels. The tuner includes bandwidth filters, amplifiers, and mixer circuits to select a desired channel or to reject unwanted channels, noise, and interference.

[0003] Television signals can be broadcast on a variety of frequencies, including ultra-high frequency (UHF), very high frequency (VHF), and high frequency (HF) frequency bands. According to the International Telecommunications Union (ITU), the UHF frequency range encompasses electromagnetic waves between 300 MHz and 3 GHz. VHF occupies frequencies in the range of approximately 30 MHz to 300 MHz, and HF occupies frequencies in the range of approximately 3 MHz to 30 MHz.

[0004] A conventional tracking filter contains multiple bandwidth filters to cover the range of possible frequencies, each tuned to a limited portion of the receiver's total bandwidth. A large tuned impedance is desirable for each filter to reduce the noise figure; however, the tuned impedance is typically a function of frequency and the size of the inductor, and this size can limit the frequency range for the respective filter.

[0005] Recently developed integrated circuit processes allow the construction of inductors with sufficiently large inductance for integration with conventional signal processing circuitry on a standard complementary metal-oxide-semiconductor (CMOS) chip. However, these inductors are relatively large, and increasing the inductance may require either making the inductor even larger or reducing its quality factor. A new receiving device capable of mitigating this conflict would be desirable.

[0006] CN 5 742 897 A discloses a highly linear radio frequency receiver with an input transformer, an output transformer, a low-noise amplifier and a matching network.

[0007] US 5 742 897 A relates to providing a matching impedance between the output of a mixer and the input of an intermediate frequency filter in a radio broadcast receiver, and more particularly to the use of a single transformer to match the impedance of both intermediate frequency filters with their corresponding mixers in a dual-band radio receiver. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present disclosure may be better understood and its numerous features and advantages may become more readily apparent to one skilled in the art by reference to the accompanying drawings, in which: Fig. 1 is a block diagram of an embodiment of a system having a receiver circuit with a tracking filter that can be configured to receive VHF LO , VHF HI and receives UHF broadcast signals; Fig.Figure 2 is a circuit diagram of a representative example of a receiving device having a conventional tracking filter with separate bandwidth filters, each tuned to a frequency band; Fig. Figure 3 is a block diagram of an embodiment of a portion of a receiver including a tracking bandwidth filter with a VHF LO -filter, a VHF HI -filter and a UHF filter; Fig. 4 a diagram of an embodiment of the VHF LO -Filters from Fig. 3 is; Fig. 5 a scheme of an embodiment of the UHF filter of Fig. 3 is; Fig. 6 an embodiment of a small-signal model of the UHF filter of Fig. 5 is; Fig. 7 is a block diagram of a low-cost television receiving apparatus according to an embodiment of the present invention; Fig. 8 shows in schematic form the VHF LO -Filter from Fig. 7 represents; Fig. 9 shows a frequency domain graph that helps to understand the function of the VHF LO -Filters from Fig. 7 to understand.

[0009] The use of the same reference symbols in different drawings indicates similar or identical things. DETAILED DESCRIPTION

[0010] Embodiments of a receiver circuit are described below, which include a small signal amplifier that receives a radio frequency signal and has an output connected to an input of a tracking filter that is configured to receive very high frequency (VHF LO and VHF HI ) and UHF broadcast signals. As used herein, VHF LO -Signals Radio frequency signals in a range of about 50 to 190 MHz, mean VHF HI-Signals are radio frequency signals in a range of approximately 190 to 470 MHz and UHF signals are radio frequency signals in a range of approximately 470 to 860 MHz. The VHF LO -Section of the tracking filter has a low-pass filter for receiving VHF LO -radio signals that uses inductive peaking to extend (or limit) the upper frequency range of the low-pass filter. The VHF LO The tracking filter section has a single-to-differential amplifier with one input connected to the output of the small-signal amplifier and with a first output and a second output. The VHF LOThe first section of the tracking filter has a bandwidth filter connected between the first and second outputs, which can be an inductive-capacitive filter. For the UHF section of the tracking filter, a transformer is used instead of a differential amplifier with a single-ended input. The transformer has a primary winding connected to the output of the small-signal amplifier and a secondary winding magnetically connected to the primary winding. The secondary winding is configured to have more turns than the primary winding to provide signal amplification between the primary and secondary windings. An example of a possible embodiment of a receiver circuit with a filter suitable for VHF LO -, VHF HI - and UHF reception is configured, is described below with reference to Fig. 1 described.

[0011] Fig.1 is a block diagram of one embodiment of a system 100 including a receiver circuit 102 with a tracking filter 110 that can be configured to receive VHF LO -, VHF HI- and UHF radio signals. The system 100 includes a signal source 104 connected to a receiver circuit 102 via an input terminal or pad 106. The signal source 104 may be an antenna, a coaxial cable, or other signal source that sends radio frequency broadcast signals to the pad 106. The receiver circuit 102 includes a front-end circuit 123 including a small signal amplifier (LNA) 108 with an input connected to the pad 106 and an output connected to an input of a tracking filter 110. The tracking filter 110 has a control input connected to a microcontroller unit 124 and an output connected to an input of a mixer 112.

[0012] The mixer 112 has inputs to receive an oscillator signal from a local oscillator 128. The mixer 112 also has an output that sends an in-phase signal to a programmable gain amplifier (PGA) 114 and an output that sends a quadrature signal to the PGA 116. The PGA 114 has an output connected to an analog-to-digital converter (ADC) 118, which has an output connected to an input of a digital filter 122. The PGA 116 has an output connected to an ADC 120, which has an output connected to an input of a digital filter 122.

[0013] The front-end circuit 123 also includes a radio frequency automatic gain control (AGC) circuit 126, which has an input connected to an output of the MCU 124 and an output connected to an input of the LNA 108. The MCU 124 is also connected to a local oscillator 128 to control the frequency of the local oscillator signals. The front-end circuit 123 also includes an intermediate frequency (IF) circuit 130, which has a control input connected to an output of the MCU 124 and outputs connected to the PGAs 114 and 116. The front-end circuit 123 also includes a low-IF circuit 132 having a control input coupled to an output of the MCU 124 and having outputs coupled to inputs of the digital filter 122.The MCU 124 is also connected to a memory 148 that can store instructions and / or data that can be used by the MCU 124 to control the operation of the front-end circuit 123.

[0014] The receiving device 102 further includes an analog television demodulator 134 with an input connected to an output of the digital filter 122 and an output connected to an input of an output interface 136. The receiving device 102 also includes a demodulator 138 for terrestrial or cable digital video broadcasting (DVB-T / C) with an input connected to the output of the digital filter 122, an input connected to an output of a digital signal processor (DSP) 144, and an output connected to an input of an equalizer 140.The equalizer 140 has an input coupled to an output of the DSP 144 and an output coupled to an input of a forward error correction (FEC) circuit 142, which has a second input coupled to an output of the DSP 144 and an output coupled to an input of an output interface 136. The DSP 144 has a control input coupled to an output of a control interface 146, which can be coupled to a host system to receive control and other signals. The control interface 146 also has an output coupled to the MCU 124.

[0015] The digital filter 122 sends the output signals to the tuner circuit, which includes an analog TV demodulator 134 and a DVB-T / C demodulator 138, which demodulate the video signal. The analog TV demodulator 134 sends the demodulated output signal to the output interface 136, which may be connected to an audio / video system on a chip or other multimedia circuit. The DVB-T / C demodulator 138 sends the output signal to the equalizer 140, which adjusts the relative strength of the selected frequencies within the demodulated output signal and sends the adjusted signal to the FEC 142. The FEC 142 uses forward error correction to correct signal errors and sends the corrected signal to the output interface 136.

[0016] In this example, the tracking filter 110 has a low-pass filter section for receiving and filtering VHF LO-broadcast signals, a second filter section for receiving and filtering VHF HI-broadcast signals and a third filter section for receiving and filtering UHF broadcast signals. In one example, the low-pass filter section comprises a single-ended input differential amplifier having an inductor / capacitor bandwidth filter at the outputs and applying inductive predistortion to expand the bandwidth range. The third section of the filter eliminates the single-ended input differential amplifier and replaces it with a transformer having a primary winding with a relatively high quality factor (Q) and a secondary winding with a much lower Q. The transformer can provide a gain of approximately 3 decibels (3 dB). By introducing gain between the primary and secondary windings, influences of limited linearity of the LNA 108 output on the linearity of the overall system are also reduced.

[0017] By adjusting the VHFLO By using the UHF and UHF filter sections, the total number of inductive-capacitive (LC) filters can be reduced by the tracking filter 110. In one example, the frequency range over which the receiving device 102 operates can be divided into an upper range, a mid-range, and a lower range of frequencies, thereby reducing the overall complexity of the tracking filter.

[0018] In conventional tracking filters, the input impedance of each filter is often designed to be large to minimize the noise figure. To maintain the high matched impedance, the inductance is increased, which limits the maximum tuned frequency of each filter. Therefore, a series of filters is used to enable filtering across the frequency range. A representative example of a receiving device using a conventional tracking filter is described below with reference to Fig. 2 described.

[0019] Fig. Figure 2 is a circuit diagram of a representative example of a receiving device 200 having a conventional tracking filter 201 with separate bandwidth filters tuned to each of the frequency bands. The receiving device 200 has an LNA 108 with an input for receiving a radio frequency input signal (RF IN ) and with an output connected to an input of the tracking filter 201.

[0020] The tracking filter 201 can have any number (N) of signal paths. In the illustrated example, a first signal path includes an inductor 202, a variable capacitor 204, a single-ended input differential amplifier 206, and a resistor 208. The inductor 202 has a first terminal connected to the input of the tracking filter 201 and a second terminal connected to ground. The capacitor 204 has a first electrode connected to the input of the tracking filter 201 and a second electrode connected to ground. The single-ended input differential amplifier 206 has an input connected to the input of the tracking filter 201, a first output connected to a first terminal of the resistor 208, and a second output connected to a second terminal of the resistor 208.

[0021] The tracking filter 201 further includes a second signal path including an inductor 212, a variable capacitor 214, a single-ended input differential amplifier 216, and a resistor 218. The inductor 212 has a first terminal connected to the input of the tracking filter 201 and a second terminal connected to ground. The capacitor 214 has a first electrode connected to the input of the tracking filter 201 and a second electrode connected to ground. The single-ended input differential amplifier 216 has an input connected to the input of the tracking filter 201, a first output connected to a first terminal of the resistor 218, and a second output connected to a second terminal of the resistor 218.

[0022] The tracking filter 201 further includes an Nth signal path including an inductor 222, a variable capacitor 224, a single-ended input differential amplifier 226, and a resistor 228. The inductor 222 has a first terminal connected to the input of the tracking filter 201 and a second terminal connected to ground. The capacitor 224 has a first electrode connected to the input of the tracking filter 201 and a second electrode connected to ground. The single-ended input differential amplifier 226 has an input connected to the input of the tracking filter 201, a first output connected to a first terminal of the resistor 228, and a second output connected to a second terminal of the resistor 228.

[0023] In one example, resistors 208, 218, and 228 are approximately ninety ohm resistors, and inductors 202, 212, and 222 have widths and lengths of approximately 600 µm x 600 µm. The input impedances (R P1 , R P2 , ..., and R PN) for each of the signal paths (1 to N) are large enough to obtain a low noise figure. In some receiving devices, the input impedances range from 400 ohms to 800 ohms. For tuned inductive LC filters, the tuned impedance is expressed as Rp=w0*L*Q, where w0 is the resonant frequency, L is the inductance, Q is the quality factor, and Rp is the input impedance. For on-chip inductors, the quality factor (Q) is essentially constant for a given range, and Q is proportional to the square root of the inductance range. To achieve the desired impedance, inductors 202, 212, and 222 are increased in size to improve Q, or the inductance value is increased to avoid increasing the inductance range. However, high inductance values ​​limit the maximum tuned frequency according to the following equation: ω max=1LN∗Cr where the variable (C T) represents a total parasitic capacitance. Unfortunately, this limitation increases the number of filters that must be included in tracking filter 201 to achieve the desired channel tuning.

[0024] To reduce the number of signal paths and thus also the number of LC filters, the tracking filter 110 extends from Fig. 1 each transfer function to cover a wider frequency band, thereby reducing the number of signal paths and thus reducing the complexity of the circuit. An example of a tracking filter that offers three transfer functions is shown below with reference to Fig. 3 described.

[0025] Fig. 3 is a block diagram of an embodiment of a portion of a receiving device 300 including a tracking filter 110 with a VHF LO -Filter 316, a VH FHI-filter and a UHF filter 320. The receiving device 300 has an LNA 108 with an input for receiving a radio frequency input signal (RF IN ) and an output connected to a source of a transistor 302. The transistor 302 has a gate connected to an output of an MCU 304 and a drain connected to an input of the tracking filter 110. The tracking filter 110 has a transistor 306 with a source connected to the input of the tracking filter 110, a gate connected to the MCU 304, and a drain connected to an input of the VHF LO -filter 316, which is implemented as a low-pass filter. The tracking filter 110 further comprises a transistor 308 with a source connected to the input of the tracking filter 110, a gate connected to the MCU 304, and a drain connected to an input of the VHF HI-filter 318. The tracking filter 110 further includes a transistor 310 having a source connected to the input of the tracking filter 110, a gate connected to the MCU 304, and a drain connected to an input of the UHF filter 320.

[0026] During operation, the MCU 304 selectively enables the signal path between the LNA 108 and one of the filters 316, 318, and 320. In one example, the MCU 304 enables transistors 302 and 306 to route the output signal of the LNA 108 to the input of the VHF LO -Filter 316. In this case, the VHF LO -Filter 316 is a low-pass filter that passes frequencies within the tuning range of approximately 50 MHz to approximately 190 MHz. There are no television channels below a frequency of 50 MHz, so the VHF LO-Filter 316 can be configured for low-pass filter operation. Towards the upper end of the range (ie as the frequency approaches approximately 190 MHz), the bandwidth of the VHF LO -Filter 316 using an inductive predistortion to extend the tuning range. An example for the VHF LO -Filter 316, which represents a possible circuit configuration, is described below with reference to Fig. 4 described.

[0027] Fig. 4 is a sketch of an embodiment of a receiving device 400, for example the receiving device 300 in Fig. 3, which the VHF LO -Filter 316. The VHF LOFilter 316 includes an inductor 402 and a resistor 403. Resistor 403 has a first terminal connected to the source of transistor 306 and a second terminal connected to a first terminal of inductor 402, which has a second terminal that is grounded. In this case, resistor 403 represents the series resistance of inductor 402. The VHF LO Filter 316 further includes a variable capacitor 404 having a first electrode connected to the drain of transistor 306 and a second electrode grounded. The VHF LOFilter 316 further includes an asymmetric-input differential amplifier 406 with a first output and a second output. Inductors 408 and 409 are connected in series between the first and second outputs. Furthermore, a variable capacitor 410 has a first electrode connected to the first output and a second electrode connected to the second output. The first and second outputs can be connected to a load, for example, a 90-ohm resistor.

[0028] In this example, the input impedance of the VHF LO-filter 316 at low frequencies is provided mainly by the series resistance of the inductor 402. At higher frequencies, the inductor 402 extends the bandwidth through inductive predistortion. The quality factor requirements are significantly alleviated by the fact that a smaller inductor can be used. However, due to the smaller inductance and the correspondingly smaller input impedance, some rejection on the upper and lower sides of the frequency band is sacrificed. To improve the rejection, the VHF LO -Filter 316, an inductive / capacitive (LC) bandwidth filter at the outputs of the single-ended input differential amplifier 406, which utilizes inductors 408 and 409 and the variable capacitor 410. Instead of using a single 600 µm x 600 µm inductor, the VHF LO-Filter 316 has three 150 µm x 150 µm inductors, which reduces the overall area of ​​the circuit, while the frequency range of the VHF LO -Filter 316 with respect to the filters in the tracking filter 201 in Fig. 2 is extended.

[0029] In the example above, the VHF uses LO -Filter 316 from Fig.3 an LC filter at the output of the single-ended differential amplifier to provide additional filtering. Since the impedance level at the output of the single-ended differential amplifier is much lower (approximately 90 ohms), small, low-Q inductors can be used to implement the bandwidth filter at the output of the single-ended differential amplifier. Thus, one high-Q bandwidth filter is replaced by two lower-Q LC filters using significantly smaller inductors, resulting in an overall reduced inductance range. The UHF filter 320 from Fig.3 eliminates the need for the active single-ended input differential amplifier, thereby reducing power consumption and improving the overall noise figure and linearity of the system. Instead of the single-ended input differential amplifier, the UHF filter 320 introduces a single-gain transformer with different Q factors between the primary and secondary inductive windings. By introducing a gain between the primary and secondary windings, the influence of the limited linearity of the LNA 108 on the linearity of the overall system is reduced. An example of a UHF filter 320 that uses a transformer instead of a single-ended input differential amplifier is described below with reference to Fig. 5 described.

[0030] Fig. 5 is a diagram of an embodiment of a receiving device 500 that incorporates the UHF filter 320 of Fig.3. In this example, the UHF filter 320 includes a variable capacitor 502 and a transformer 504. The variable capacitor 502 has a first electrode connected to the drain of the transistor 310 and a second electrode that is grounded. The transformer 504 includes a primary inductive winding 506 with a first terminal connected to the drain of the transistor 310 and a second terminal connected to a source voltage (e.g., a voltage approximately midway between the supply voltage rails, denoted as "V MID The transformer 504 further includes a secondary inductive winding 508 having a first terminal and a second terminal that may be connected to the mixer 112 and that has a grounded center tap.

[0031] In the illustrated example, the primary inductive winding 506 has a Q value that is higher than the Q value of the secondary inductive winding 508. Furthermore, the transformer 504 introduces a gain from the primary inductive winding 506 to the secondary inductive winding 508. In one case, the gain is approximately 3 dB. In one example, the secondary inductive winding 508 of the transformer 504 has more turns than the primary inductive winding 506, thereby maintaining the gain.

[0032] In a specific embodiment, the primary inductive winding 506 is formed from approximately 3.4 µm of high-quality copper (Cu), for example, Cu M8, and approximately 2.8 µm of aluminum (Al). In this embodiment, the secondary inductive winding 508 is formed from lower-quality metal, for example, Cu M4 or M5, and each comprises approximately 0.2 µm of Cu. The primary and secondary inductive windings 506 and 508 may be patterned in redistribution layers of the semiconductor substrate. The secondary inductive winding 508 is formed from lower-quality metals to improve the natural frequency response of the transformer 504. Furthermore, the coupling coefficient is very strong (approximately k=1). A small-signal model of an example of the UHF filter 320 is described below with reference to Fig. 6 described.

[0033] Fig. 6 is an embodiment of a small signal model 600 of the UHF filter of Fig.5. The small-signal model 600 has an input voltage terminal 602 for receiving an input voltage (v in ) and an output voltage terminal 604 for supplying an output voltage (v out ). The small signal model 600 has a variable capacitor 606 connected between the input voltage source 602 and ground. The variable capacitor 606 can be a variable capacitor 502 in Fig. 5 as well as a parasitic capacitance of the primary winding 506 of the transformer 504 in Fig. 5. The small-signal model 600 further includes an inductor 608 and a resistor 610 connected in series between the input voltage terminal 602 and ground. The secondary winding 508 of the transformer 504 in Fig.5 is modeled as an inductor 614 and a resistor 616 connected in series between the output voltage terminal 604 and ground. A secondary capacitor 618 is also connected between the output voltage source 604 and ground.

[0034] Assuming that the primary inductive winding 506 is tuned to a resonant frequency (ω0) while the secondary inductive winding 508 is untuned, then the resonant frequency of the secondary winding (ω s ) much larger than the resonance frequency (ω0), as follows: ωs=1L614C618 where L 614 represents the inductance of the inductor 614 and C 618 represents the capacitance of capacitor 618. The coupling between the primary and secondary inductive windings 506 and 508 is very strong (k is approximately 1). The current flowing into the secondary winding (i s ), is determined according to the following equation: is=−jωMip1jωC618+jωL614+R616=−jωMip11−ω2L614C618jωC618+R616 where R 616 represents the resistance of resistor 616, the frequency (ω) represents the input frequency and the variable (M) is determined by the following equation: M=kL608L614

[0035] Since k=1, for frequencies close to the resonant frequency (ω0), the current flowing into the secondary winding 508 can be determined according to the following equation: is=ipω2MC6141+jωR616C618 where i s is the current flowing in the secondary inductive winding, and i p is the current flowing in the primary inductive winding 506.

[0036] In the example shown, the input voltage (v in ) is determined using the following equation: vin=(jwL608+R610)ip+jωMω2MC6181+jωR616C618ip and the effective impedance (Z eff), which looks into the primary winding of the transformer, is determined as follows: Zeff=vinip=jωL608+R610+ω2M2jωC6181+jωR616C618

[0037] In equation 7, the factor jωL 608 +R 610 the impedance due to the primary inductive winding 506, and the remaining part of the equation is the impedance due to the secondary inductive winding 508. Suppose the factor ωR 616 C 618 is much smaller than 1, then the effective impedance (Z eff ) can be simplified as follows: Zeff=jωL608+R610+ω2M2jωC618(1−jωR616C618)= jω(L608+ω2M2C618)+R610+ω4M2C6182R6162

[0038] The effective impedance, which is due to the inductance, (L eff ), is determined according to the following equation: Leff=L608+ω2M2C618=L608(1+ω2L614C618)=L608(1+ω2ωs2)

[0039] The effective impedance, which is due to the resistance value, (R eff ), is determined according to the following equation: Reff=R610+ω4M2C6182R616=R610+(ωωs)4L608L614R616

[0040] If in the above examples the ratio of the resonance frequency (ω0) to the frequency (ω s ) is kept small, then the secondary inductive winding 508 has a limited effect on the tuned frequency of the primary inductive winding 506. Furthermore, by keeping this ratio small, the effect of the secondary inductive winding on the quality factor (Q) is also kept small. For example, if the ratio is about 1 / 3 and the resistance value (R 616 ) is about ten times the resistance of resistor 610, and if the inductances of inductors 608 and 614 are approximately equal, then the effective quality factor (Q eff ) can be determined using the following equation: Qeff≅0.99ωL608R610

[0041] On the secondary side there is also the output voltage (v out ) with the input voltage (v in ) according to the following equation: vout=vinL614L608

[0042] Equation 12 shows a conversion gain in the transformer 504. It can be seen that the secondary inductive winding 508 acts as an inductive / capacitive (LC) low-pass filter at higher frequencies in addition to the LC bandwidth characteristics of the primary inductive winding 506.

[0043] Thus, the single-ended to differential conversion that can be achieved by a prior art single-ended input differential amplifier can be replaced by performing the conversion magnetically using a transformer 504 having a secondary inductive winding 508 with a low quality factor. The effect of the secondary inductive winding 508 on the quality factor of the primary inductive winding 506 is proportional to the fourth power of the frequency. Accordingly, the quality factor, and hence the gain, of the LNA 108 decreases with increasing tuned frequency, which helps reduce the gain deviation in the transfer function of the UHF filter 320. As previously discussed, it is also possible to implement a conversion gain greater than 0 dB by adjusting the number of turns used to obtain gain on the secondary inductive winding 508.By introducing such gain, the transformer 504 acts to lower the signal level at the output of the LNA 108, thereby improving the third order band intersection (IIP3) of the LNA 108 since the gain is provided in the transformer 504.

[0044] In connection with the above with reference to Fig. 1 - 6, a receiving device is disclosed which has a tracking filter with a reduced number of LC filters compared to conventional tracking filters for television reception. More specifically, the tracking filter divides the frequency range into three bands (VHF LO , VHF HI , and UHF) and provides a low-pass filter for the VHF LO frequencies, a bandwidth filter for the VHF HI frequencies and a transformer-based bandwidth filter for the UHF broadcast signals.

[0045] Fig.Figure 7 is a block diagram of a low-cost television receiver 700 according to an embodiment of the present invention. Receiver 700 generally includes a low-noise amplifier (LNA) 710, a switch section 720, a filter section 730, a mixer and combiner 740, an amplifier section 750, an analog-to-digital converter (ADC) section 760, a digital signal processor and demodulator section 770, and a microcontroller 780.

[0046] The LNA 710 has an input for receiving the input signal RF IN and an output to provide an amplified RF IN-signal. The switch section 720 includes three N-channel transistors 722, 724, and 726. The transistor 722 has a first source / drain terminal connected to the output of the LNA 710 and a second source-drain terminal. The transistor 724 has a first source / drain terminal connected to the output of the LNA 710 and a second source-drain terminal. The transistor 726 has a first source / drain terminal connected to the output of the LNA 710 and a second source-drain terminal.

[0047] The filter section 730 has a first filter labeled “VHF LO FILTER” 732, a second filter labeled “VHF HIFILTER" 734, and a third filter, labeled "UHF FILTER" 736. Filter 732 has an input connected to the second terminal of transistor 722, a tuning input, and an output at which a filtered difference signal is provided. Filter 734 has an input connected to the second terminal of transistor 724, a tuning input, and an output at which a filtered difference signal is provided. Filter 736 has an input connected to the second terminal of transistor 726, a tuning input, and an output at which a filtered difference signal is provided.

[0048] The mixer / combiner 740 has inputs connected to corresponding outputs of the filters 732, 734 and 736, a first output providing an in-phase difference signal labeled "I", and a second output providing a square difference signal labeled "Q".

[0049] The amplifier section 750 includes programmable gain amplifiers (PGAs) 752 and 754. The PGA 752 has a differential input connected to the first output of the mixer / combiner 740, a gain control input, and a differential output. The PGA 754 has a differential input connected to the second output of the mixer / combiner 740, a gain control input, and a differential output.

[0050] The ADC section 760 includes ADCs 762 and 764. The ADC 762 has a differential input connected to the output of the PGA 752 and a multi-bit digital output. The ADC 764 has a differential input connected to the output of the PGA 754 and a multi-bit digital output.

[0051] The digital signal processor and demodulator 770 has a first input connected to the output of the ADC 762, a second input connected to the output of the ADC 764, and an output at which a signal is output that is labeled “TV OUT “ is marked.

[0052] The MCU 780 has a first output connected to the gate of transistor 722, a second output connected to the gate of transistor 724, a third output connected to the gate of transistor 726, and a set of outputs connected in Fig.7 are not specifically shown and are connected to various other blocks which will be described later.

[0053] In operation, the receiver 700 is part of a highly integrated, low-cost television receiver. The LNA 710 receives the RF IN -Signal from an antenna or other signal source (in Fig. 7 not shown), and outputs the amplified RF IN signal to one of three signal processing paths, which is selected depending on the frequency band and the desired channel. In response to a tuning input (in Fig.7 not shown), the MCU 780, under firmware control, selects the appropriate signal processing path by activating one of the signals driving the gates of the transformers 722, 724, and 726. If the desired channel is in the 50-190 MHz range, the MCU 780 in the receiver 700 activates the signal to the gate of the transformer 722, and the receiver 700 forms the VHF LO -Filters 732 TV OUT from the amplified RF IN signal. If the desired channel is in the 190-470 MHz range, the MCU 780 activates the signal to the gate of the transformer 724, and the receiver 700 forms the TV OUT -Filters 734 TV OUT from the amplified RF INsignal. Filter 734 is a parallel resonant LC filter and has a differential converter with an asymmetric input. If the desired channel is in the 470-860 MHz range, MCU 780 enables the signal to the gate of transformer 726, and receiver 700 forms TV using UHF filter 736. OUT from the amplified RF IN -signal. The filter 736 is implemented as described above with reference to Fig. 5 and Fig. 6 described.

[0054] The receiver 700 is suitable for low-cost applications using various techniques. First, the receiver 700 is fully integrated on a single integrated circuit chip using on-chip conductors currently available in state-of-the-art CMOS processes without expensive external components. Second, only three bands are used for the filter section 730 instead of the five bands used for the receiver 200 of Fig.2. Third, the UHF filter 736 uses an on-chip transformer in conjunction with a variable capacitor to perform both bandwidth filtering and differential conversion from an unbalanced input, thereby saving circuit space required by an additional amplifier and also extending the dynamic range of the receiving device 700.

[0055] Fourthly, the VHF uses LO Filter 732 comprises a low-Q RLC filter and a low-Q LC bandwidth filter, which occupy a smaller area than a conventional parallel resonant LC filter while providing most of the advantages of such a filter. The structure and characteristics of this filter will now be described.

[0056] Fig. Figure 8 shows in schematic form the VHF LO -Filter of 732 Fig.7. The filter 732 generally comprises an RLC low-pass filter 800, an amplifier 830, and a bandwidth filter 840. The filter 800 comprises a variable capacitor 810 and an inductance branch 820. The variable capacitor 810 comprises a fixed capacitor 812, a binary-coded capacitor 814, and a thermometer-coded capacitor 816. The fixed capacitor 812 has a first terminal to supply the amplified RF IN signal, and a second terminal that is grounded. The binary-coded capacitor 814 has a first terminal for receiving the amplified RF IN signal, a second terminal that is grounded, and a tuning input terminal that receives a binary-coded tuning signal. The thermometer-coded capacitor 816 has a first terminal for receiving the amplified RF INsignal, a second terminal that is grounded, and a tuning input terminal that receives a thermometer-encoded tuning signal. The inductance branch 820 has a resistor 822 and an inductor 824. The resistor 822 has a first terminal to receive the amplified RF IN signal, and a second terminal. The inductor 824 has a first terminal connected to the second terminal of the resistor 822 and a second terminal connected to V MID The effective resistance of the inductance branch 820 is equal to a resistance value of the resistor 822 plus a parasitic resistance of the inductance 824.

[0057] The amplifier 830 has a first input terminal for receiving the amplified RF IN signal, a second input terminal connected to a terminal marked “V AG", and first and second output terminals that provide a differential output signal pair. V AG is an analog ground voltage, which is usually midway between the more positive and ground.

[0058] Bandwidth filter 840 includes a variable capacitor 850 and a differential inductor 860. Variable capacitor 850 includes two fixed capacitors 851 and 852, two binary-coded capacitors 853 and 844, and two thermometer-coded capacitors 855 and 856. Capacitor 851 has a first terminal connected to the first output terminal of amplifier 850 and a second terminal connected to ground. Capacitor 852 has a first terminal connected to ground and a second terminal connected to the second output terminal of amplifier 830. Capacitor 853 has a first terminal connected to the first output terminal of amplifier 830, a second terminal connected to ground, and a tuning input terminal that receives a binary-coded tuning signal.Capacitor 854 has a first terminal connected to ground, a second terminal connected to the second output terminal of amplifier 830, and a tuning input terminal that receives a binary-coded tuning signal. Capacitor 855 has a first terminal connected to the first output terminal of amplifier 830, a second terminal connected to ground, and a tuning input terminal that receives a thermometer-coded tuning signal. Capacitor 856 has a first terminal connected to ground, a second terminal connected to the second output terminal of amplifier 830, and a tuning input terminal that receives a thermometer-coded tuning signal.

[0059] The differential inductor 860 includes inductors 862 and 864. The inductor 862 has a first terminal connected to the first output terminal of the amplifier 830 and a second terminal connected to V AGThe inductor 864 has a first terminal connected to V AG and a second terminal connected to the second output terminal of amplifier 830.

[0060] In operation, the 732 filter acts as a bandpass filter and differential converter with an unbalanced input for the amplified RF IN signal when the user selects a channel in VHF LO-Band from 50 MHz to 190 MHz. However, instead of simply providing a variable cutoff frequency within this band, the low-pass filter 732 provides some selectivity in a narrower frequency band centered on the desired channel. Thus, the low-pass filter 732 provides some of the benefits of a bandwidth filter without requiring high-quality (and thus expensive) on-chip inductors. At the same time, the filter 732 significantly attenuates higher frequency components, helping to maintain a good signal-to-noise ratio that would otherwise cause parasitic admixture of unwanted energy in the passband.

[0061] The resonance frequency of the filter 800 (“f R “) is obtained as follows: fR=12π(1LC)⋅1+2R2CL−(RL)2 where L represents the inductance of inductor 824, C represents the capacitance of variable capacitor 810, and R represents the resistance of resistor 822. The 3 dB bandwidths around f R (“BW”) is obtained by: BW=12π⋅RL

[0062] Table I below shows the values ​​of the various components used in the RLC filter 800 for the VHF LO -Filter band: TABLE I element Value Fixed capacitor 812 1.63 pF Binary coded capacitor 814 15 x 9.4 fF Thermometer-coded capacitor 816 31 x 150 fF Resistance 822 396 Ω Inductance 824 465 nH where pF is picoFarad, fF is femtoFarad, Ω is ohm, and nH is nanoHenry. Note that the 396 Ω resistance of resistor 822 is formed from a 345 Ω parasitic resistance of inductor 824 along with a separate 54 Ω resistor.

[0063] Table II below shows the values ​​of the various components used in the RLC filter 800 for the VHF LO -Filter band: TABLE II element Value Fixed capacitors 851 and 852 10 pF Binary coded capacitors 853 and 854 15 x 150 fF Thermometer-coded capacitors 855 and 856 31 x 2.4 pF Parasitic resistance of the inductance 824 28 Ω Inductance 824 86 nH

[0064] Using a currently available 0.55 micrometer CMOS manufacturing process with copper metallization and eight available metal layers, in the VHF LO -Filter 732, the inductor 824 is formed in a mold surface of 150 micrometers (µm) x 150 µm and the inductor 860 is formed on a semiconductor die surface of 280 µm x 160 µm. As already stated above, the VHF LO -Bandwidth filter of the receiver 200 of Fig. 2, however, a semiconductor wafer surface of about 600 µm x 600 µm. Thus, the VHF LO -Filter 732 used inductors with the lower Q-value only about 19% of the semiconductor die surface of the inductor with the higher Q-value used for the VHF LO -Bandwidth filter from Fig.2 is used. The filter 732 actually uses the parasitic resistance in the inductor 824 to determine the size of the other components at a given f R Thus, filter 732 achieves most of the advantages of a parallel resonant bandwidth filter, but on a significantly smaller die surface area, helping to keep receiver 700 inexpensive.

[0065] Fig. Figure 9 shows a frequency domain graph that helps to understand the function of the VHF LO -Filters from Fig. 7 to understand. In Fig. 9, the vertical axis represents the gain in decibels (dB), while the horizontal axis represents the frequency on a logarithmic scale in Hz. A first waveform 910 corresponds to the frequency response of the RLC filter 800 and is relatively flat, but with a small dip of about 2-3 dB below f R, it shows a relatively constant decrease with increasing frequency for frequencies above f R and has a peak at a resonance frequency f R The peak is for f R near the upper end of the VHF LO -band is small, but increases to about 6 dB for f R at the upper end of the VHF LO -Band (the case described in Fig. 9).

[0066] A second waveform 920 corresponds to the frequency response of the bandwidth filter 840 and is for lower frequencies below f R essentially flat, but shows a relatively constant decrease with increasing frequency for frequencies above f R and has a peak of about 4-6 dB at a resonance frequency f R The peak is for f R near the lower end of the VHF LO -band is about 4 dB and increases to about 6 dB for f R at the upper end of the VHF LO-Band.

[0067] A third waveform 930 corresponds to the overall frequency response to the VHF LO -Filter 732 and is for frequencies below f R relatively flat with a small dent, shows a relatively constant decrease with increasing frequency for frequencies above f R and has a peak of 4-10 dB at a resonance frequency f R The peak is for f R near the lower end of the VHF LO -band is about 4 dB and increases to about 10 dB for f R at the upper end of the VHF LO -band. Thus, the addition of the bandwidth filter 840 ensures a certain selectivity for frequencies near f R for frequencies at the lower end of the VHF LO -Band.

[0068] Thus, the receiver 700 is highly integrated and remains inexpensive by using on-chip inductors. The size of the inductor in the VHF LOThe 10-band filter can be kept small by implementing an unbalanced filter as an RLC filter, in which the resistance is formed partly by the parasitic resistance of an on-chip inductor and partly by a separate integrated resistor. The receiving device 700 adds an additional parallel resonant LC filter passband with a slightly higher-quality inductor to provide additional selectivity in the passband.

[0069] The above-disclosed subject matter is intended to be considered illustrative, not restrictive, and the appended claims are intended to cover all modifications, improvements, and other embodiments that fall within the true scope of the claims. Therefore, to the extent permitted by law, the scope of the present invention is to be determined by the broadest possible interpretation of the following claims and their equivalents, and is not to be restricted or limited by the foregoing detailed description.

Claims

[1] Receiving device (300), comprising: a first amplifier (108) having an input for receiving a radio frequency signal and having an output; a first variable capacitor (502) having a first terminal connected to the output of the first amplifier and a second terminal connected to a first supply voltage terminal; and a transformer (504) comprising: a primary winding (506) having a first terminal connected to the first terminal of the first variable capacitor and a second terminal connected to a second supply voltage terminal, and a secondary winding (508) having a first terminal and a second terminal for outputting a filtered radio frequency difference signal, the secondary winding having a greater number of turns than the primary winding. [2] A receiving device according to claim 1, wherein a quality factor of the primary winding is greater than a quality factor of the secondary winding. [3] Receiving device according to one of claims 1 to 2, wherein: the primary winding is made of copper and aluminum; and the secondary winding is made of copper. [4] A receiving device according to any one of claims 1 to 3, wherein the secondary winding is formed of a thinner metal than the primary winding. [5] Receiving device according to one of claims 1 to 4, wherein the secondary winding acts as a second-order inductive-capacitive low-pass filter. [6] Receiving device (700), comprising: a first amplifier (710) having an input for receiving a radio frequency signal and an output; and a first filter (732) comprising: a first variable capacitor (810) having a first terminal connected to the output of the first amplifier, a second terminal connected to a supply voltage terminal, and a control terminal for receiving a tuning signal; and an inductance branch (820) having a first terminal connected to the output of the first amplifier and a second terminal connected to the supply voltage terminal, the inductance branch including a first inductance (824) and having a resistance in series with the first inductance, the resistance having a value related to an upper threshold value for the frequency of the first filter. [7] Receiving device according to claim 6, further comprising: a second filter (734) having an input coupled to the output of the first amplifier, a tuning input, and an output for substantially passing frequencies within a band above a lower threshold frequency of the second filter and below an upper threshold frequency of the second filter. [8] Receiving device according to claim 7, further comprising: a third filter (736) having an input coupled to the output of the first amplifier, a tuning input, and an output for substantially passing frequencies within a band above a lower threshold frequency of the third filter. [9] A receiving device according to claim 8, wherein the third filter comprises: a third variable capacitor (502) having a first terminal connected to the output of the first amplifier and a second terminal connected to a second supply voltage terminal; and a transformer (504) comprising: a primary winding (506) having a first terminal connected to the first terminal of the third variable capacitor and a second terminal connected to a third supply voltage terminal, and a secondary winding (508) having a first terminal and a second terminal for outputting a filtered radio frequency difference signal. [10] Receiving device according to one of claims 7 to 9, wherein the receiving device characterized by is that it is a television receiver. [11] Receiving device according to one of claims 9 to 10, wherein: both the upper threshold frequency of the first filter and the lower threshold frequency of the second filter are approximately 190 megahertz (MHz); and both the upper threshold frequency of the second filter and the lower threshold frequency of the third filter are approximately 470 MHz. [12] Receiving device according to one of claims 7 to 11, wherein the inductance branch (820) comprises: a resistor (822) having a first terminal connected to the output of the first amplifier and a second terminal connected to a first terminal of the first inductance (824), wherein the effective resistance of the inductance branch is equal to a resistance value of the resistor plus a parasitic resistance of the first inductance. [13] Receiving device according to one of claims 7 to 12, further comprising: a second amplifier (830) having an input connected to the output of the first amplifier and first and second outputs forming a differential signal pair; a second variable capacitor (850) having a first terminal connected to the first output of the second amplifier, a second terminal connected to the second output of the second amplifier, and a tuning input terminal; and a second inductance (860) having a first terminal connected to the first output of the second amplifier and a second terminal connected to the second output of the second amplifier. [14] A receiving device according to claim 13, wherein the output of the first amplifier and the input of the second amplifier are unbalanced. [15] Receiving device (700), comprising: a first amplifier (710) having an input for receiving a radio frequency signal and having an output; and a first filter (732) connected to the output of the first amplifier for passing components of the radio frequency signal below a first frequency threshold, the first filter comprising: an asymmetrical input differential amplifier (830) having an input connected to the output of the first amplifier via a low-pass filter (800), and having a first output and a second output. and a bandwidth filter (840) connected between the first and second outputs. [16] A receiving device according to claim 15, wherein the low-pass filter further comprises: a first variable capacitor (810) having a first terminal connected to the output of the first amplifier, a second terminal connected to a supply voltage terminal, and a control terminal for receiving a tuning signal; and an inductance branch (820) having a first terminal connected to the output of the first amplifier and a second terminal connected to the supply voltage terminal, the inductance branch including a first inductance (824) and having a resistance in series with the first inductance, the resistance having a value related to an upper threshold value for the frequency of the first filter. [17] A receiving device according to claim 16, wherein the inductance branch comprises: a resistor (822) having a first terminal connected to the output of the first amplifier and a second terminal connected to a first terminal of the first inductance, wherein the effective resistance of the inductance branch is equal to a resistance of the resistor plus a parasitic resistance of the first inductance. [18] A receiving device according to claim 16, wherein the first variable capacitor (810) comprises: a fixed capacitor (812) having a first terminal connected to the output of the first amplifier and a second terminal connected to the supply voltage terminal; a binary capacitor (814) having a first terminal connected to the output of the first amplifier, a second terminal connected to the supply voltage terminal, and a control terminal for receiving a binary-coded tuning signal; and a thermometer-coded capacitor (816) having a first terminal connected to the output of the first amplifier, a second terminal connected to the supply voltage terminal, and a control terminal for receiving a thermometer-coded signal. [19] A receiving device according to claim 15, wherein the bandwidth filter (840) comprises: a variable capacitor (850) having a first electrode connected to the first output and a second electrode connected to the second output a second inductance (860) having a first terminal connected to the first output of the second amplifier and a second terminal connected to the second output of the second amplifier.

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