Os motores de busca de Datasheet de Componentes eletrônicos |
|
AD6458 Folha de dados(PDF) 11 Page - Analog Devices |
|
AD6458 Folha de dados(HTML) 11 Page - Analog Devices |
11 / 12 page AD6458 –11– REV. 0 MXP 275 Ω 275 Ω 25k Ω VBIAS 160k Ω MXM VPOS FROM MIXER CORE MXOP 330 Ω Figure 32. Mixer Output Port IF Amplifier Most of the gain in the AD6458 resides in the IF amplifier strip, which comprises two stages. Both are fully differential and each has a gain span of 26 dB for the AGC voltage range of 0.2 V to 2.25 V. Thus, in conjunction with the variable gain of the mixer, the total gain span is 76 dB. The overall IF gain varies from –9 dB to 48 dB for the nominal AGC voltage of 0.2 V to 2.25 V. Maximum gain is at VGAIN = 0.2 V. The IF input is differential at IFIP and IFIM. Figure 33 shows a simplified schematic of the IF interface modeled as parallel RC network. The IF’s small-signal bandwidth is approximately 50 MHz from IFIP and IFIM through the demodulator. IFHI IFLO CSH RSH Figure 33. IF Amplifier Port Modeled as a Parallel RC Network Gain Scaling The AD6458’s overall gain, expressed in decibels, is linear with respect to the AGC voltage VGAIN at pin GAIN. The gain of all sections is maximum when VGAIN is 0.2, and falls off as the bias is increased to VGAIN = 2.25 and is independent of the power supply voltage. The gain of all stages changes simultaneously. The AD6458’s gain scaling is also temperature compensated. The GAIN pin of the AD6458 is an input driven by an external low impedance voltage source, normally a DAC, under the control of radio’s digital processor. The gain-control scaling is directly proportional to the reference voltage applied to the pin GREF and is independent of the power supply voltage. When this input is set to the nominal value of 1.2 V, the scale is nominally 27 mV/dB (37 dB/V). Under these conditions, 76 dB of gain range (mixer plus IF) corresponds to a control voltage of 0.2 V <= VG <= 2.25 V. The final centering of this 2.05 V range depends on the insertion losses of the IF filters used. Pin GREF can be tied to an external voltage reference, VREF, provided, for example, by a AD1580 (1.21 V) voltage reference. AD6458 IRXP IRXN QRXP QRXN GREF GAIN FREF AD6421 100pF 100pF 100pF 100pF 0.1µF 160 Ω 1nF VCTCXO IRXP IRXN QRXP QRXN BREFOUT BREFCAP AGC DAC AFC DAC Figure 34. Interfacing the AD6458 to the AD6421 Baseband Converter When using the Analog Devices AD7013 (IS54, TETRA and satellite receiver applications) and AD7015 or AD6421 (GSM, DCS1800, PCS1900) baseband converters, the external ref- erence may also be provided by the reference output of the baseband converters. The interface between the AD6458 and the AD6421 baseband converter is shown in Figure 34. The AD6421 baseband converter provides a VREF of 1.23 V; an auxiliary DAC in the AD6421 can be used to generate the AGC voltage. Since it uses the same reference voltage, the numerical input to this DAC provides an accurate RSSI value in digital form, no longer requiring the reference voltage to have high absolute accuracy. I/Q Demodulators Both demodulators (I and Q) receive their inputs internally from the IF amplifiers. Each demodulator comprises a full-wave synchronous detector followed by an 8 MHz, two-pole low-pass filter, producing differential outputs at pins IRXP and IRXN, and QRXP and QRXN. Using the I and Q demodulators for IFs above 50 MHz is precluded by the 5 MHz to 50 MHz range of the PLL used in the demodulator section. The I and Q outputs are differential and can swing up to 2.2 V p-p at the low supply voltage of 3.0 V. They are nominally centered at 1.5 V independently of power supply. They can therefore directly drive the RX ADCs in the AD6421 baseband converter, which require an amplitude of 1.23 V to fully load them when driven by a differential signal. The conversion gain of the I and Q demodulators is 17 dB. For IFs of less than 8 MHz, the on-chip low-pass filters (8 MHz cutoff) do not adequately attenuate the IF or feedthrough prod- ucts; the maximum input voltage must thus be limited to allow sufficient headroom at the I and Q outputs, not only for the de- sired baseband signal but also the unattenuated higher order demodulation products. These products can be removed by an external low-pass filter. A simple 1-pole RC filter, with its cor- ner above the modulation bandwidth, is sufficient to attenuate undesired outputs. The design of the RC filter is eased by the 4.7 k Ω resistor integrated at each I and Q output pin. |
Nº de peça semelhante - AD6458 |
|
Descrição semelhante - AD6458 |
|
|
Ligação URL |
Privacy Policy |
ALLDATASHEETPT.COM |
ALLDATASHEET é útil para você? [ DONATE ] |
Sobre Alldatasheet | Publicidade | Contato conosco | Privacy Policy | roca de Link | Lista de Fabricantes All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |