AD607ARS datasheet(16/24 Pages) AD

16 / 24 page

REV. C

–16–

AD607

The IF’s small-signal bandwidth is approximately 45 MHz from

IFHI and IFLO through IFOP. The peak output at IFOP is

± 560 mV at V

P = 3 V and

± 400 mV at the minimum V

P of

2.92 V. This allows some headroom at the demodulator inputs

(Pin DMIP), which accept a maximum input of

±150 mV for

IFs > 3 MHz and

±75 mV for IFs ≤ 3 MHz (at IFs ≤ 3 MHz,

the drive to the demodulators must be reduced to avoid saturat-

ing the output amplifiers with higher order mixing products that

are no longer removed by the on-board low pass filters).

Since there is no band-limiting in the IF strip, the output-

referred noise can be quite high; in a typical application and

at a gain of 75 dB, it is about 100 mV rms, making post-IF filtering

desirable. IFOP may be also used as an IF output for driving

an A/D converter, external demodulator, or external AGC

detector. Figure 17 shows methods of matching the optional

second IF filter.

AD607

BPF

IFOP

DMIP

2RT

VPOS

a. Biasing DMIP from Power Supply (Assumes BPF

AC-Coupled Internally)

AD607

BPF

IFOP

DMIP

VMID

CBYPASS

b. Biasing DMIP from VMID (Assumes BPF AC-Coupled

Internally)

Figure 17. Input and Output Matching of the Optional

Second IF Filter

Gain Scaling and RSSI

The AD607’s overall gain, expressed in decibels, is linear-in-dB

with respect to the AGC voltage VG at Pin GAIN. The gain of

all sections is maximum when VG is zero, and reduces progres-

sively up to VG = 2.2 V (for VP = 3 V; in general, up to a limit

VP – 0.8 V). The gain of all stages changes in parallel. The AD607

features temperature compensation of the gain scaling. The gain

control scaling is proportional to the reference voltage applied to

the Pin GREF. When this pin is tied to the midpoint of the

supply (VMID), the scale is nominally 20 mV/dB (50 dB/V) for

VP = 3 V. Under these conditions, the lower 80 dB of gain range

(mixer plus IF) corresponds to a control voltage of 0.4 V

≤

≤ 2.0 V. The final centering of this 1.6 V range depends on

the insertion losses of the IF filters used. More generally, the gain

scaling using these connections is VP/150 (volts per dB), so scale

becomes 33.3 mV/dB (30 dB/V) using a 5 V supply, with a

proportional change in the AGC range, to 0.33 V

≤ VG ≤ 3 V.

Table II lists gain control voltages and scale factors for power

supply voltages from 2.92 V to 5.5 V

Alternatively, Pin GREF can be tied to an external voltage

reference (VR) from, for example, an AD1582 (2.5 V) or

AD1580 (1.21 V) voltage reference, to provide supply-

independent gain scaling of VR/75 (volts per dB). When using

the Analog Devices’ AD7013 and AD7015 baseband converters,

the external reference may also be provided by the reference

output of the baseband converter (Figure 18). For example, the

AD7015 baseband converter provides a VR of 1.23 V; when

connected to GREF, the gain scaling is 16.4 mV/dB (60 dB/V).

An auxiliary DAC in the AD7015 can be used to generate the

MGC 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.

AD607

IOUT

QOUT

VMID

GREF

10nF

GAIN

1nF

AD7013 OR

AD7015

IADC

QADC

IADC

QADC

REFOUT

BYPASS

(AD7015)

(AD7013)

AUX DAC

Figure 18. Interfacing the AD607 to the AD7013 or AD7015

Baseband Converters

I/Q Demodulators

Both demodulators (I and Q) receive their inputs at Pin DMIP.

Internally, this single-sided input is actually differential; the

noninverting input is referenced to Pin VMID. Each demodula-

tor comprises a full-wave synchronous detector followed by a

2 MHz, two-pole low-pass filter, producing single-sided outputs

at pins IOUT and QOUT. Using the I and Q demodulators for

IFs above 12 MHz is precluded by the 400 kHz to 12 MHz

response of the PLL used in the demodulator section. Pin DMIP

requires an external bias source at VP/2; Figure 19 shows

suggested methods.

Outputs IOUT and QOUT are centered at VP/2 and can swing

up to

±1.23 V even at the low supply voltage of 2.92 V. They can

therefore directly drive the RX ADCs in the AD7015 baseband

converter, which require an amplitude of 1.23 V to fully load

them when driven by a single-sided signal. The conversion gain of

the I and Q demodulators is 18 dB (X8), requiring a maxi-

mum input amplitude at DMIP of

±150 mV for IFs > 3 MHz.

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