RFMD2080 Datasheet, PDF (8/19 Pages) RF Micro Devices – 45MHz TO 2700MHz IQ MODULATOR WITH SYNTHESIZER/VCO AND BASEBAND INTERFACE`

RFMD2080
I_p
I_n
10K
10K
rc_tune
dcdac_ai
dcdac_i
DAC
DAC
I
bb_atten
cal_blank
Q_p
Q_n
10K 10K
rc_tune
rc_tune
dcdac_aq
dcdac_q
DAC
DAC
Q
bb_atten
cal_blank
rc_tune
The differential I and Q input impedance is set by 10K pull down resistors on each pin, so presenting 20K differential
impedance. The baseband input signals will be typically 1Vp-p differential. A common mode DC voltage between 0.5V and 1.5V
is required for optimal performance. If required the phase and amplitude of either of the I or Q signal can be adjusted to
reduce the level of the unwanted sideband signal at the modulator output.
The baseband path consists of an active low pass filter with variable capacitors. The variable capacitors provide 64 "rctune"
settings that allow the input 3dB bandwidth to be tuned from 1.5MHz to 10MHz. This is followed by a variable gain attenuator
that delivers 0dB to -20dB gain in 2dB steps. Additionally, the mixers have gain control, ranging from 0dB to -18dB in 6dB
steps giving a maximum range of 38dB. The variable gain attenuator and mixer input have DACs attached to allow DC offsets
within the baseband path to be corrected, thus reducing LO breakthrough. An isolation switch sits between the variable gain
attenuator and the mixer input to allow their offsets to be compensated separately. This may be required since the offset within
the variable gain attenuator will vary with gain and thus its DC compensation may also have to vary for optimum LO cancella-
tion.
Serial Interface
All on-chip registers in the RFMD2080 are programmed using a proprietary 3-wire serial bus which supports both write and
read operations. Synthesizer programming, device configuration and control are achieved through a mixture of hardware and
software controls. Hardware pins can be used to control ENBL, MODE and RESETX or the device can be programmed entirely
via the serial bus.
The serial data interface can be configured for 4-wire operation, by setting the '4WIRE' bit in the SDI_CTRL register high. Then
pin 26 is used as the data out pin, and pin 32 is the serial data in pin.
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DS140110