Building a better, lower cost, smarter TV/STB tuner - Embedded.com

Building a better, lower cost, smarter TV/STB tuner

This “Product How-To” article focuses how to use a certain product in an embedded system and is written by a company representative.

Most tuners in TV and STB applications use thetraditional single conversionmixeroscillator PLL (MOPLL) concept. This concept is able to handle analog or digital TVsignals, or both at the same time (so-called hybrid tuners). Keyfactors to be considered when designing such tuners are lowcost, low power consumption, small form factor, and the choice of theexternal tuner components.

This article elaborates how to achieve an ultralow-cost (ULC) tunerreference design using the Infineon MOPLL tuner TUA 6039-2 or itsmirrored version TUA 6037. This ULC tuner integrates the RF and IFstages in a single chip. It operates at either 5V or 3.3V, hencereducing power consumption by 34 percent.

The design uses a single-sided PCB that reduces system cost, and isable to handle hybrid signals including DVB-T/ PAL/SECAM,ISDB-T/NTSC and ATSC/NTSC standards thatcover almost all global regions. This reference design reduces the timebetween development and mass production, and thus improves time tomarket.

Tuner details
The block diagram of the single conversion tuner with TUA 6039-2/ TUA6037 is shown in Figure 1 below.

Figure1: Block diagram of single conversion tuner with TUA 6039-2/TUA 6037 isshown.

It is not only an RF tuner but also half network interface module(NIM) since it includes the IF block. The RF input signal is split by asimple high pass filter combined with IF and CB traps.

Instead of band switching with PIN diodes, a very simple triplexercircuit is used. With a high inductive coupling, the antenna impedanceis transformed to the tuned input circuits. The pre-selected signal isthen amplified by the high gain semi-biased Infineon MOSFET BF5030W.One BG5120K, Dual- MOSFET can be used for both VHF bands.

In the following tuned band-pass filter stage, the channel isselected and unwanted signals such as adjacent channels and imagefrequency are rejected. Tracking traps of pre-stages and capacitiveimage frequency compensation of band filters especially reject imagefrequencies.

The TUA 6039-2 is a full 3-band tuner IC that has all the activeparts for the three mixers, three oscillators, a SAW driver and an IFamplifier. The complete PLL functions include four pnp ports and onenpn port for the band switching, and a wideband AGC detector forinternal tuner AGC.

Combined with the optimized loop filter, four programmable chargepump currents, the balanced crystal oscillator and the voltagecontrolled oscillators (VCO), the half NIM can achieve phase noiseperformance suitable for all digital applications.

The balanced IF output signal of the TUA 6039-2 is designed todirectly drive a SAW filter in the following IF stage. The signal fromthe SAW is further amplified by the gain-controlled on-chip amplifierand its output signal can be used directly by the demodulator IC in thefollowing stage. Also, the conversion to IF is also performed with thechip.

Power gains
The half NIM consumes less than 130mA current or 650mW power with +5Vsupply voltage. Using a +3.3V power supply, the total power consumed isonly 429mW. This low power consumption is a big advantage for portableand handheld applications.

Figure2: Single-layer PCB design for a hybrid tuner with TUA 6039-2/TUA 6037is shown

The single-layer PCB design of this ULC tuner is well-received bythe TV tuner market. The cost difference between a single- and atwo-layer PCB is important for the total BOM of a tuner. The resultingPCB design is shown in Figure 2 above .The PCB used for the half NIM design is single-sided, 1.6mm thick FlameRetardant 4 material.

Figure 3 below shows thecompleted reference design. Standard dimensions were used, but thesedimensions can be reduced further.

This single-layer PCB reference design exhibits good performance forhybrid reception of TV signals following the PAL/DVB-T, NTSC/ATSC andNTSC/ISDB-T standards. Other standards, including T-DMB, DAB, DMB-TH,DVB-C and Open Cable, can also be processed.

The good performance is directly attributed to the IC itself. ThePLL loop filter and its post filter need to be configured according tothe chosen standard—pure digital (e.g. DVB-T), pure analog (e.g.PAL/SECAM) or hybrid (e.g. DVB-T + PAL/SECAM).

Figure3: Reference design of the ultralow-cost tuner with single-layer PCB.

The 62.5kHz reference frequency rejection ratio is based on adifferent loop filter and its post filter configuration. Although theloop filter can be modified in order to cover both 166.67kHz and62.5kHz for hybrid purposes, there is a compromise between phase noise,reference frequency rejection and PLL lock-in time.

It is strongly recommended that designers select the referencefrequency first (62.5kHz, 166.67kHz or both) before adopting therelevant loop filter and post filter configuration.

The results of the measurements show that the single-layer PCB tunerdesign in hybrid mode was able to achieve a reference frequencyrejection ratio of 60dB and higher. This rejection ratio complies withthe requirements of analog receivers.

Packaging challenge
One of the challenges faced while developing the reference design wasthe adaptation of the PCB for the VQFN package. Having only one layerfor the connections and grounding reduced flexibility for thegrounding.

In RF design, grounding is vital, and this was the major challengefor the tuner design. The most critical electrical parameter influencedby the grounding is the rejection of spurious signals from the crystal;PLL reference frequency and DC/DC converter which is also integrated inthe ULC tuner.

The design achieved DC/DC clock spurious rejection ratio of about52dB and VCO reference frequency spurious rejection ratio of 60dB.

Another issue arising from the use of a single-layer PCB and VQFNpackage is the dissipation of heat produced by the IC. In order tohandle and improve heat dissipation, the reference design was made in away that allows access to the backside of the IC.

Thus, thermal dissipation can be improved, for example by the frameof the tuner. Furthermore this tuner can operate at 3.3V; hencereducing power consumption and heat.

There is an ever increasing need for RF tuners in multimedialifestyle applications; and manufacturers are demanding smaller formfactors, lower power consumption and cost reduction.

The design of this ULC tuner is an effort to obtain an optimumbetween cost, performance and power consumption. Using the TUA 6039-2as the core element of the hybrid tuner achieves good performance at apower saving 3.3V supply.

Furthermore, the cost reduction due to the single layer PCB designcan be considered as the icing on the cake. This ULC tuner referencedesign from Infineon Technologies reduces risk and improves producttime to market without compromising performance and quality.

Claus Muschallik is director, Tuner Systems and TV ReceiverSystem Support, Infineon TechnologiesAsia Pacific Pte. Ltd.

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