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SA1920 датащи(PDF) 6 Page - NXP Semiconductors |
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SA1920 датащи(HTML) 6 Page - NXP Semiconductors |
6 / 36 page Philips Semiconductors Product specification SA1920 Dual-band RF front-end 1999 Mar 02 6 OPERATION The low-band contains both an LNA and mixer that is designed to operate in the 800 to 1000 MHz frequency range. The high-band contains an LNA and image-rejection mixer that is designed to operate in the 1800 to 2000 MHz frequency range with over 30 dB of rejection over an intermediate frequency (IF) range from 100 to 125 MHz. Image rejection is achieved in the internal architecture by two RF mixers in quadrature and two all-pass filters in the I and Q IF channels that phase shift the IF by 45 _ and 135_, respectively. The two phase shifted IFs are recombined and buffered to produce the IF output signal. The LO section consists of an internal all-pass type phase shifter to provider quadrature LO signals to the receive mixers. The all-pass filters outputs are buffered before being fed to the receive mixers. The transmit mixer section consists of a low-noise amplifier, and a down-convert mixer. In the transmit mode, an internal LO buffer is used to drive the transmit IF down-convert mixer. Low-Band Receive Section The circuit contains a LNA followed by a wide-band mixer. In a typical application circuit, the LNA output uses an external pull-up inductor to VCC and is AC coupled. The mixer IF outputs are differential. A typical application will load the output buffer with an inductor across the IF outputs, a pull-up inductor to VCC and an AC coupled capacitor to the matching network. Low-Band Receive Section (Analog Transmit Mode) The bias current of the low-band LNA will increase during analog transmission, which increases its gain compression point and makes the receiver less sensitive to PA leakage power for an AMPS application. High-Band Receive Section The circuit contains an LNA followed by two high dynamic range mixers. These are Gilbert cell mixers; the internal architecture is fully differential. The LO is shifted in phase by 45 _ and 135_ and mixes the amplified RF signal to create I and Q channels. The two I and Q channels are buffered, phase shifted by 45 _ and 135_, respectively, amplified and recombined internally to realize the image rejection. The IF output is differential and of the open-collector type. A typical application will load the output buffer with an inductor across the IF outputs, a pull-up inductor to VCC and an AC coupled capacitor to the matching network. Control Logic Section Pins HI/LO, SYN ON, Rx On, Tx On, Strong Signal, X2 (doubler) On, control the logic functions. The HI/LO mode selects between low-band and high-band operation. The SYN ON mode enables the LO buffers independent of the other circuitry. When SYN ON is high, all internal buffers in the LO path of the circuit are turned on, thus minimizing LO pulling when the remainder of the receive or transmit chain is powered-up. The Rx ON mode enables the LO buffers when the device is in the low-band receive normal, receive strong signal and transmit modes; the Rx ON mode enables the LO buffers, also, when the device is in the high-band receive normal, and receive strong signal modes. The Tx ON mode enables the transmit mixer. The strong signal mode, when disabled, allows the low- and high-band LNAs to function normally; and when the strong signal mode is enabled, it turns-off the low- and high-band LNAs. This is needed when the input signal is large and needs to be attenuated. The doubler (X2) on mode enables the doubler. When the doubler is on, the input signal from the LO buffers is doubled in frequency. The signal can be used to drive the image-rejection mixer and the output LO high-band ports. When the doubler mode is on, all other control logic (see table 1) functions the same. Local Oscillator (LO) Section The LO input directly drives the two internal all-pass networks to provide quadrature LO to the receive mixers. A synthesizer-on (SYN ON) mode is used to power-up all LO input buffers, thus minimizing the pulling effect on the external VCO when entering receive or transmit mode. Transmit Mixer Section The transmit mixer is used for down-conversion to the transmit IF. Its inputs are coupled to the transmit RF which is down-converted to a modulated transmit IF frequency, and phase-locked with the baseband modulation. The IF outputs are HIGH impedance (open-collector type). A typical application will load the output buffer with an inductor across the IF outputs, a pull-up inductor to VCC and AC coupled capacitors to the matching network. |
Аналогичный номер детали - SA1920 |
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Аналогичное описание - SA1920 |
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