RF2722_1 Datasheet, PDF (17/26 Pages) RF Micro Devices – GSM/GPRS/EDGE RECEIVER

Proposed
RF2722
Application Information
Functional Description
The RF2722 receiver IC will support GSM and EDGE cellular standards.
Four Low Noise Amplifiers (LNA’s) are provided to accommodate various combinations of up to four bands. The four LNA’s
share a common quadrature mixer. The active LNA is selected and may be bypassed through the Serial Data Interface (SDI).
An RX Local Oscillator (VCO) is provided. The VCO is fully integrated including an internal resonator and is band-selectable to
cover the GSM850, EGSM, DCS, and PCS bands.
The desired signal is converted to either a VLIF (100kHz/120kHz) or directly to DC, as determined by the setting of bit 1 in SDI
register CF.
Once downconverted, the signal is filtered by an active RC Polyphase bandpass filter. The purpose of this filter is to provide
some rejection to interfering signals such that the dynamic range of the A/D converters will not be compromised.
The RF2722 also includes two reverse isolation dual-band buffer amplifiers. These buffers are suitable for use in the transmit
path between the VCO output and the PA input to improve transmit performance. The RF2722 accepts single-ended inputs
from the RF6001/3 and provides single-ended outputs to the PA.
DC Correction Operation
The Polaris RF2722 VLIF/DCR IC will reduce the residual DC error of the I and Q channels to less than 20mV within 20usec
assuming that no input signal is present during the DC adapt time. The DC correction system will activate on the rising edge of
RX_EN if the SDI bit DC_EN is programmed true. Programming the SDI bit DC_ST true can also activate the DC correction sys-
tem. In this case the SDI bit DC_ST will automatically return to a false state once the DC correction system is activated.
The RF6001/3 also has an RX_EN pin that normally is set high at the same time as the RX_EN of the RF2722.
The DC correction system of the RF2722 will run for DC_TIME1 cycles of the clock present on CLK_IN divided by 16. This
should be set for approximately 20usec. With a 26MHz clock on CLK_IN the setting of DC_TIME1 will be 20H. Given the low
levels of LO leakage to the LNA inputs of the RF2722, the coarse DC adapt will be performed when RX_EN rises with the LNAs
disabled. The residual DC error due to LO leakage when the LNAs are enabled will be less than 5mV. Once completed the DC
correction outputs of the RF2722 will be held until power is removed from the IC or until another DC correction command is
issued.
During operation of the DC correction system the input signal should be muted so that the coarse DC correction system does
not attempt to lock to the instantaneous signal level. This can be accomplished by disabling all LNAs. This mode is selected if
the LND SDI bit is programmed true. This is performed for DC_TIME2 clock cycles of CLK_IN divided by 16 beginning at the DC
correction command time so that the RF2722 will have sufficient time to complete DC correction.
If the radio employs a T/R switch then the T/R switch can also be used to disable the signal instead of or in addition to dis-
abling the LNAs. The RF2722 can be used to automatically disable the T/R switch if the SDI bit TRD is programmed true. In this
case it is assumed that GPO1 and GPO2 provide on/off control for each of the possible bands of the receive side of the T/R
switch. During the DC control time interval set by DC_TIME2 the outputs of GPO1 and GPO2 will be overridden by the SDI regis-
ter TRDC. The bits of this register can be set to 0 or 1 as needed by the particular T/R switch implementation to deactivate the
receiver inputs. After DC_TIME2 has expired the normally programmed GPO states will return.
After the coarse DC adapt time has elapsed then the RF6001/3 will require an additional time of approximately 50usec to
complete the fine digital DC correction.
Note that the input signal may be present during the final DC correction time of the RF6001/3. For VLIF modes this will not
cause a DC problem since the RF6001/3 does an averaging of the DC error and there will be few components of the signal
Rev A4 DS050919
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at ([phone] or [e-mail].
17 of 26