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TDA8041H Datasheet(PDF) 6 Page - NXP Semiconductors |
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TDA8041H Datasheet(HTML) 6 Page - NXP Semiconductors |
6 / 16 page November 1994 6 Philips Semiconductors Preliminary specification Quadrature demodulator controller TDA8041H GENERAL DESCRIPTION The quadrature demodulator controller TDA8041H, generates all control signals required for demodulation of BPSK and QPSK modulated signals. This device is specially designed to be used in conjunction with the quadrature demodulator IC, TDA8040T. The quadrature demodulator controller generates the following signals: • Symbol clock recovery control signal; this signal locks the VCXO to the received symbol clock. The clock recovery algorithm used in this device operates independently from the other loops. • Carrier recovery control signal; depending on the selected mode (BPSK or QPSK), this signal will adjust the phase of the I and Q input signal. This adjustment will be such that the constellation points are as defined in Fig.4. • Frequency control signals (AFC1 and AFC2); to serve a broad range of applications, two different AFC detectors and a sweep function are built-in: – AFC1: this is a robust detector which forces the offset frequency in the I and Q branch to zero. This detector can handle frequency offset up to 1/8 × symbol rate. – AFC2: this detector can handle frequency offsets greater than 1/8 × symbol frequency. However this AFC algorithm will bring the offset frequency only close to zero. – Sweep: this signal generates a triangular current output which can tune a VCO over its complete frequency range. Sweeping must be switched off as soon as the logical output of the lock detect function becomes positive. The value of the sweep current is set by an external resistor. • Amplitude control signals (AGC); this signal adjusts a variable gain amplifier so that the amplitude of the I and Q signals is in accordance with the specified constellation points of Fig.4. • Lock detect signal; this signal is related to the Eb/No of the incoming I and Q signals. This lock detect signal can be used for two purposes: – Lock detection by comparing the lock detect signal with an external set reference voltage, one can obtain a logical signal indicating lock detect. – The relationship between Eb/No can be used to display the Eb/No for antenna adjustment. FUNCTIONAL DESCRIPTION The TDA8041H has a 3-bit-wide digital I and Q output for soft error correction. These 3-bit outputs represent the main symbols only. The relationship between the 4-bits ADC signals and the 3-bit output signals is illustrated in Fig.3. Fig.3 I and Q output levels for soft error decision FEC. |
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