AD607ARS datasheet(19/24 Pages) AD

19 / 24 page

REV. C

–19–

AD607

As noted earlier, the gain in dB is reduced linearly with the voltage

VG on the GAIN pin. Figure 23 shows how the mixer and IF strip

gains vary with VG when GREF is connected to VMID (1.5 V) and

a supply voltage of 3 V is used. Figure 24 shows how these vary

when GREF is connected to a 1.23 V reference.

(7.5dB)

(1.5dB)

01V

0.4V

1.8V

2.2V

(67.5dB)

(21.5dB)

IF GAIN

MIXER GAIN

90dB

80dB

70dB

60dB

50dB

40dB

30dB

20dB

10dB

0dB

NORMAL OPERATING RANGE

Figure 23. Gain Distribution for GREF = 1.5 V

(7.5dB)

(1.5dB)

01V

(67.5dB)

(21.5dB)

IF GAIN

MIXER GAIN

90dB

80dB

70dB

60dB

50dB

40dB

30dB

20dB

10dB

0dB

0.328V

1.64V

NORMAL OPERATING RANGE

Figure 24. Gain Distribution for GREF = 1.23 V

Using the AD607 with a Fast PRUP Control Signal

If the AD607 is used in a system in which the PRUP signal

(Pin 3) is applied with a rise time less than 35

µs, anomalous

behavior occasionally occurs. The problem is intermittent, so it

will not occur every time the part is powered up under these

conditions. It does not occur for any other normal operating condi-

tions when the PRUP signal has a rise time slower than 35

µs.

Symptoms of operation with too fast a PRUP signal include low

gain, oscillations at the I or Q outputs of the device, or no valid

data occurring at the output of the AD607. The problem causes

no permanent damage to the AD607, so it will often operate

normally when reset.

Fortunately, there is a very simple solution to the fast PRUP

problem. If the PRUP signal (Pin 3) is slowed down so that

the rise time of the signal edge is greater than 35

µs, the

anomalous behavior will not occur. This can be realized by a

simple RC circuit connected to the PRUP pin, where R = 4.7 k

Ω

and C = 1.5 nF. This circuit is shown in Figure 25.

AD607

PRUP

4.7k

1.5nF

FROM PRUP

CONTROL SIGNAL

Figure 25. Proper Configuration of AD607 PRUP Signal

All designs incorporating the AD607 should include this circuitry.

Note that connecting the PRUP pin to the supply voltage will

not eliminate the problem, since the supply voltage may have a

rise time faster than 35

µs. With this configuration, the 4.7 kΩ

series R and 1.5 nF shunt C should be placed between the

supply and the PRUP pin as shown in Figure 25.

AD607 EVALUATION BOARD

The AD607 evaluation board (Figures 26 and 27) consists of an

AD607, ground plane, I/O connectors, and a 10.7 MHz band-

pass filter. The RF and LO ports are terminated in 50

Ω to

provide a broadband match to external signal generators to

allow a choice of RF and LO input frequencies. The IF filter is

at 10.7 MHz and has 330

Ω input and output terminations; the

board is laid out to allow the user to substitute other filters for

other IFs.

The board provides SMA connectors for the RF and LO port

inputs, the demodulated I and Q outputs, the manual gain con-

trol (MGC) input, the PLL input, and the power-up input. In

addition, the IF output is also available at an SMA connector;

this may be connected to the PLL input for carrier recovery to

realize synchronous AM and FM detection via the I and Q

demodulators, respectively. Table III lists the AD607 Evalua-

tion Board’s I/O Connectors and their functions.

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