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ACE9020KG bảng dữ liệu(PDF) 4 Page - Zarlink Semiconductor Inc |
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ACE9020KG bảng dữ liệu(HTML) 4 Page - Zarlink Semiconductor Inc |
4 / 6 page 4 ACE9020 Figure 3 - ACE9020 Test circuit Description The ACE9020 is designed for use in a transceiver such as an analog cellular phone, which uses an offset modulation transmit architecture. The circuit consists of a VHF voltage controlled oscillator to generate the offset frequency, an upconverter to transmit frequency and also a prescaler for the main UHF phase locked loop. The Rxvcoin signal to the ACE9020 is normally the UHF local oscillator used for downconversion. A basic block diagram is shown in fig. 2, further information on external connections is provided in the test circuit (fig. 3) and the applications diagram (fig. 4). VHF Oscillator This oscillator is a differential design which uses an external tank circuit as shown in fig. 3 and fig. 4. The components shown in fig. 3 give a VCO frequency of 90MHz. A varactor diode is coupled capacitively to the tank circuit; the anode is referenced to ground via a resistor. The VCO control from a synthesiser (eg ACE9030) charge pump output is applied to the cathode of the varactor also through a resistor. These resistors should be the same value to keep the differential circuit balanced. The VCO gain with the components shown will be typically 2 MHz/V. Modulation is applied to the anode via a resistive divider as shown in fig. 4; the actual signal applied to the varactor will be small as the frequency deviation will typically be a maximum of 12kHz in many applications. Differential buffered outputs from the oscillator (TXOSC) interface directly to the ACE9030 auxiliary synthesier inputs. Upconverter An image reject mixer is used for the upconversion. This provides typically 20dB rejection of the unwanted upper sideband. The quadrature networks for the mixer are all provided on chip; this is optimised for UHF local oscillator and VHF offset oscillator frequencies typically used for analog cellular phones on the AMPS and TACS systems. Further filtering of the TXPA output will be required to provide further suppression of the unwanted upper sideband, local oscillator signal and harmonics to meet cellular telephone specifications. SAW filters are available for the various transmit frequency bands. The upconverter outputs (TXPA + and -) are differential current outputs. The use of differential outputs minimises current switching within the device and thus minimise cross- talk to other circuit blocks. The TXPA outputs must be matched to the external filter, normally 50 Ωand single-ended. The network shown in fig. 3 provides a transformation from 400 Ω differential to 50Ω single-ended and also provides dc bias from the Vcc supply to the open collector TXPA outputs. This network provides plus and minus 90 ° phase shift in each output which are then summed. Alternatively a Balun transformer could be used, it will again be necessary to provide dc bias to the TXPA outputs. The load to the current outputs should be maximised to obtain the maximum power output; 400 Ω is an optimum figure as higher values require impractical component values for matching. Prescaler The two modulus prescaler is part of the UHF phase locked loop. It will typically be operating with ACE9030 radio interface and synthesiser. There is also a choice of divider ratio, set by the ratio select input as shown in table. 1, below. The differential divider outputs can be directly coupled to the ACE9030 main synthesiser inputs. ACE9020 Rxvcoin 22k 18k Vcc Vcc VCO Control TXOsc Div Out + - + - + TXPA - 27n 27n 18n 1p 27p 1p Tx Output 100p 100p 18p 100n BB545 6k8 6k8 5,12,21,25,28 10 11 23 48 3,9,13, 18,22 16 15 19 20 6 7 Mod Cntrl Ratio Sel 14 17 PD1 12 PD2 faux = 90 MHz Ratio Sel Ratio Sel = LOW = HIGH Mod_Cntrl = LOW ÷129 ÷65 Mod_Cntrl = HIGH ÷128 ÷64 Table 1 |
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Mô tả tương tự - ACE9020KG |
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