Specifications

Circuit Description
DS360 Ultra Low Distortion Function Generator
6-8
U503). Q503, Q504 and Q506 are configured as a cascode, to maintain a constant
voltage across U503. Q501 and Q502 are active collector loads for U503 A and B. Q507
provides a low impedance source to Q508, which provides most of the voltage gain. It is
biased at 3.5 mA by Q509.
Output transistors Q512 and Q513 are configured as a class B amplifier (push-pull).
However, Q510 and Q511 bias them slightly on, to reduce crossover distortion. P502 sets
the bias current through Q512 and Q513.
Output Attenuators and Source Resistance
Relay K601 can select the + and - signals for normal operation, or ground for switching
the outputs off. Relays K602, K603 and K604 select output attenuation of 0dB, 20dB,
40dB or 60dB for both the + and - outputs. The attenuator chain has an output resistance
of 25Ω. Relays K605, K606 and K607 select an additional resistance, that together with
the attenuator output resistance, provides the desired source resistance.
U601, U603, U606, U608, U610 are latches for most of the relays in the analog section.
U602, U604, U605, U607, U609, Q601, Q602 and Q603 are drivers for all relays. All
relays are latching type, so the drivers output a brief +5 V pulse (~4 ms) to set or clear
each relay.
Power Supply
The analog board is floating relative to the chassis or the digital board. It is AC coupled
to ground through C790-C796 and R705 on the analog board. There is additional
coupling on the output board.
J701 brings power from the main transformer to the analog board. D701, D702 rectify
the AC voltages into unregulated DC voltages that are filtered by C703-C706 and C719-
C722. U701 (LM317) and U702 (LM337) are adjustable voltage regulators, programmed
for ±28 V
DC
. L701-L704 and C711-C718 provide high frequency filtering for the output
voltage. U703 (LM7815) and U704 (LM7915) are fixed ±15 V
DC
voltage regulators.
Their outputs are filtered by L705-L708 and C725-C732.
U705 (LM7805) provides +5 V
DC
to most of the logic circuitry on the analog board.
U709 (LM7805) and U707 (LM7905) provide ±5 V
DC
to the square wave circuitry. R706
and R707 are dropping resistors, to minimize the power dissipated in U709 and U707.
U706 (LM78L12) and U708 (LM79L12) provide power to the waveform DAC.
C741-C749 are bypass capacitors for the +5 V logic (U705). C755-C759 are bypass for
the square wave +5 V (U709). C770-C775 are bypass for +28 V. C780-C785 are bypass
for -28 V. C776-C777 are bypass for +15 V. C786-C787 are bypass for -15 V.