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TDA9889TS bảng dữ liệu(PDF) 6 Page - NXP Semiconductors |
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TDA9889TS bảng dữ liệu(HTML) 6 Page - NXP Semiconductors |
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6 / 22 page  2004 Nov 02 6 Philips Semiconductors Product specification DVB selective AGC amplifier TDA9888TS; TDA9889TS Reference generation The 4 MHz crystal is the reference for the downconversion synthesizer and the filter synthesizer. The downconverted DVB frequency and the frequency adjustment of the integrated filters are dependent on the precision of the reference signal at pin REF. An operation as crystal oscillator is possible as well as connecting this input via a serial capacitor to another low-ohmic reference frequency source. The integrated divider-by-8 generates the internally needed 500 kHz reference frequency for the DVB synthesizer and the reference filter. Synthesizer for downconversion The PLL synthesizer for downconversion consists of a Voltage Controlled Oscillator (VCO), a divider with a standard dependent divider factor, a frequency phase detector (constructed as a digital 3-state comparator) and a charge pump. The VCO operates as an integrated low radiation relaxation oscillator at double the conversion frequency. For downconversion the VCO frequency is divided-by-2 to provide two differential square wave signals with exactly 90 degrees phase difference, independent of the VCO frequency. The frequency phase detector compares the down-divided oscillator signal with the 500 kHz reference frequency signal and controls, via the charge pump, the control voltage at the external loop filter connected to pin LFS, which is required to tune the VCO exactly to the wanted frequency. The divider, the frequency phase detector and the reference frequency divider are constructed in a low radiation technique to optimize the synthesizer spurious suppression in the downconverted output signal. Downconversion and complex filtering The gain controlled IF signal from the IF amplifier is fed to two identical linear mixers, operating in the ‘in phase’ and ‘quadrature’ mode in accordance to the 0 and 90 degree VCO signal from the synthesizer. With this, the downconverted DVB low IF signal is available as an I and Q signal in the frequency band from 1 to 9 MHz. These signals are fed to the complex filter section. As a result of adding both signals, the unwanted mirror signal will be attenuated (approximately 34 dB). The unwanted frequency components below 1 MHz are attenuated in a high-pass filter. This signal is then fed through a group-delay equalizer circuit. Tracking low-pass filter with reference control The low-pass filter is controlled by a reference signal [generated by a frequency synthesizer and can be switched by the standard selection (S0 and S1)]. The tracking low-pass filter is designed as a Tschebyscheff filter to guarantee sufficient suppression for the neighbouring picture carrier. An all-pass filter corrects the characteristic to obtain a flat (equivalent ripple) group delay behaviour. Low IF differential output stage The output amplifier consists of two identical differential operational amplifiers with a high common mode (DC) rejection ratio, to provide a constant DC voltage at the output stage. The amplified Low IF (LIF) signal is available as a differential signal with an amplitude of 2 V (p-p) and DC level of 2 V (typ.) between the output terminals of both amplifiers. Logic control The logic control provides an easy selection of the most common standards for Europe, USA and Japan with the two switches S0 and S1 (frequency selection different for TDA9888TS and TDA9889TS) and controls all internal standard dependent stages. The five available tuner AGC modes can be set via the 3-state input pin S2 and RTOP connection (at pin TADJ). Internal voltage stabilizer The band gap circuit generates a voltage of approximately 2.4 V, independent of the supply voltage and the temperature. A voltage regulator circuit, controlled by this voltage, produces a constant voltage of 3.55 V which is used as an internal reference voltage. |
Số phần tương tự - TDA9889TS |
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Mô tả tương tự - TDA9889TS |
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